The Impact of Starbursts on the Circumgalactic Medium. (arXiv:1303.1183v2 [astro-ph.CO] UPDATED):
We present a study exploring the impact of a starburst on the properties of
the surrounding circum-galactic medium (CGM): gas located beyond the galaxy's
stellar body and extending out to the virial radius (200 kpc). We obtained
ultraviolet spectroscopic data from the Cosmic Origin Spectrograph (COS)
probing the CGM of 20 low-redshift foreground galaxies using background QSOs.
Our sample consists of starburst and control galaxies. The latter comprises
normal star-forming and passive galaxies with similar stellar masses and impact
parameters as the starbursts. We used optical spectra from the Sloan Digital
Sky Survey(SDSS) to estimate the properties of the starbursts, inferring
average ages of 200 Myrs and burst fractions involving ~10% of their stellar
mass. The COS data reveal highly ionized gas traced by CIV in 80%(4/5) of the
starburst and in 17%(2/12) of the control sample. The two control galaxies with
CIV absorbers differed from the four starbursts in showing multiple
low-ionization transitions and strong saturated Lyman-alpha lines. They
therefore appear to be physically different systems. We show that the CIV
absorbers in the starburst CGM represent a significant baryon repository. The
high detection rate of this highly ionized material in the starbursts suggests
that starburst-driven winds can affect the CGM out to radii as large as 200
kpc. This is plausible given the inferred properties of the starbursts and the
known properties of starburst-driven winds. This would represent the first
direct observational evidence of local starbursts impacting the bulk of their
gaseous halos, and as such provides new evidence of the importance of this kind
of feedback in the evolution of galaxies.
Showing posts with label Starburst. Show all posts
Showing posts with label Starburst. Show all posts
Sunday, March 10, 2013
Saturday, February 23, 2013
Star Formation and Gas Kinematics of Quasar Host Galaxies at z~6: New insights from ALMA. (arXiv:1302.4154v1 [astro-ph.CO])
Star Formation and Gas Kinematics of Quasar Host Galaxies at z~6: New insights from ALMA. (arXiv:1302.4154v1 [astro-ph.CO]):
We present ALMA observations of the [C II] 158 micron fine structure line and
dust continuum emission from the host galaxies of five redshift 6 quasars. We
also report complementary observations of 250 GHz dust continuum and CO (6-5)
line emission from the z=6.00 quasar SDSS J231038.88+185519.7. The ALMA
observations were carried out in the extended array at 0.7" resolution. We have
detected the line and dust continuum in all five objects. The derived [C II]
line luminosities are 1.6x10^{9} to 8.8x10^{9} Lsun and the [C II]-to-FIR
luminosity ratios are 3.0-5.6x10^{-4}, which is comparable to the values found
in other high-redshift quasar-starburst systems and local ultra-luminous
infrared galaxies. The sources are marginally resolved and the intrinsic source
sizes (major axis FWHM) are constrained to be 0.3" to 0.6" (i.e., 1.7 to 3.5
kpc) for the [C II] line emission and 0.2" to 0.4" (i.e., 1.2 to 2.3 kpc) for
the continuum. These measurements indicate that there is vigorous star
formation over the central few kpc in the quasar host galaxies. The ALMA
observations also constrain the dynamical properties of the atomic gas in the
starburst nuclei. The intensity-weighted velocity maps of three sources show
clear velocity gradients. Such velocity gradients are consistent with a
rotating, gravitationally bound gas component, although they are not uniquely
interpreted as such. Under the simplifying assumption of rotation, the implied
dynamical masses within the [C II]-emitting regions are of order 10^{10} to
10^{11} Msun. Given these estimates, the mass ratios between the SMBHs and the
spheroidal bulge are an order of magnitude higher than the mean value found in
local spheroidal galaxies, which is in agreement with results from previous CO
observations of high redshift quasars.
We present ALMA observations of the [C II] 158 micron fine structure line and
dust continuum emission from the host galaxies of five redshift 6 quasars. We
also report complementary observations of 250 GHz dust continuum and CO (6-5)
line emission from the z=6.00 quasar SDSS J231038.88+185519.7. The ALMA
observations were carried out in the extended array at 0.7" resolution. We have
detected the line and dust continuum in all five objects. The derived [C II]
line luminosities are 1.6x10^{9} to 8.8x10^{9} Lsun and the [C II]-to-FIR
luminosity ratios are 3.0-5.6x10^{-4}, which is comparable to the values found
in other high-redshift quasar-starburst systems and local ultra-luminous
infrared galaxies. The sources are marginally resolved and the intrinsic source
sizes (major axis FWHM) are constrained to be 0.3" to 0.6" (i.e., 1.7 to 3.5
kpc) for the [C II] line emission and 0.2" to 0.4" (i.e., 1.2 to 2.3 kpc) for
the continuum. These measurements indicate that there is vigorous star
formation over the central few kpc in the quasar host galaxies. The ALMA
observations also constrain the dynamical properties of the atomic gas in the
starburst nuclei. The intensity-weighted velocity maps of three sources show
clear velocity gradients. Such velocity gradients are consistent with a
rotating, gravitationally bound gas component, although they are not uniquely
interpreted as such. Under the simplifying assumption of rotation, the implied
dynamical masses within the [C II]-emitting regions are of order 10^{10} to
10^{11} Msun. Given these estimates, the mass ratios between the SMBHs and the
spheroidal bulge are an order of magnitude higher than the mean value found in
local spheroidal galaxies, which is in agreement with results from previous CO
observations of high redshift quasars.
Sunday, February 17, 2013
The evolution of the AGN content in groups up to z~1. (arXiv:1302.2861v1 [astro-ph.CO])
The evolution of the AGN content in groups up to z~1. (arXiv:1302.2861v1 [astro-ph.CO]):
Determining the AGN content in structures of different mass/velocity
dispersion and comparing them to higher mass/lower redshift analogs is
important to understand how the AGN formation process is related to
environmental properties. We use our well-tested cluster finding algorithm to
identify structures in the GOODS North and South fields, exploiting the
available spectroscopic redshifts and accurate photometric redshifts. We
identify 9 structures in GOODS-south (presented in a previous paper) and 8 new
structures in GOODS-north. We only consider structures where at least 2/3 of
the members brighter than M_R=-20 have a spectroscopic redshift. For those
group members that coincide with X-ray sources in the 4 and 2 Msec Chandra
source catalogs respectively, we determine if the X-ray emission originates
from AGN activity or it is related to the galaxies' star-formation activity. We
find that the fraction of AGN with Log L_H > 42 erg/s in galaxies with M_R <
-20 is on average 6.3+-1.3%, much higher than in lower redshift groups of
similar mass and more than double the fraction found in massive clusters at a
similarly high redshift. We then explore the spatial distribution of AGN in the
structures and find that they preferentially populate the outer regions. The
colors of AGN host galaxies in structures tend to be confined to the green
valley, thus avoiding the blue cloud and, partially, also the red-sequence,
contrary to what happens in the field. We finally compare our results to the
predictions of two sets of semi analytic models to investigate the evolution of
AGN and evaluate potential triggering and fueling mechanisms. The outcome of
this comparison attests the importance of galaxy encounters, not necessarily
leading to mergers, as an efficient AGN triggering mechanism. (abridged)
Determining the AGN content in structures of different mass/velocity
dispersion and comparing them to higher mass/lower redshift analogs is
important to understand how the AGN formation process is related to
environmental properties. We use our well-tested cluster finding algorithm to
identify structures in the GOODS North and South fields, exploiting the
available spectroscopic redshifts and accurate photometric redshifts. We
identify 9 structures in GOODS-south (presented in a previous paper) and 8 new
structures in GOODS-north. We only consider structures where at least 2/3 of
the members brighter than M_R=-20 have a spectroscopic redshift. For those
group members that coincide with X-ray sources in the 4 and 2 Msec Chandra
source catalogs respectively, we determine if the X-ray emission originates
from AGN activity or it is related to the galaxies' star-formation activity. We
find that the fraction of AGN with Log L_H > 42 erg/s in galaxies with M_R <
-20 is on average 6.3+-1.3%, much higher than in lower redshift groups of
similar mass and more than double the fraction found in massive clusters at a
similarly high redshift. We then explore the spatial distribution of AGN in the
structures and find that they preferentially populate the outer regions. The
colors of AGN host galaxies in structures tend to be confined to the green
valley, thus avoiding the blue cloud and, partially, also the red-sequence,
contrary to what happens in the field. We finally compare our results to the
predictions of two sets of semi analytic models to investigate the evolution of
AGN and evaluate potential triggering and fueling mechanisms. The outcome of
this comparison attests the importance of galaxy encounters, not necessarily
leading to mergers, as an efficient AGN triggering mechanism. (abridged)
X-ray Detections of Sub-millimetre Galaxies: Active Galactic Nuclei Versus Starburst Contribution. (arXiv:1302.0842v1 [astro-ph.GA])
X-ray Detections of Sub-millimetre Galaxies: Active Galactic Nuclei Versus Starburst Contribution. (arXiv:1302.0842v1 [astro-ph.GA]):
We present a large-scale study of the X-ray properties and near-IR-to-radio
SEDs of submillimetre galaxies (SMGs) detected at 1.1mm with the AzTEC
instrument across a ~1.2 square degree area of the sky. Combining deep 2-4 Ms
Chandra data with Spitzer IRAC/MIPS and VLA data within the GOODS-N/S and
COSMOS fields, we find evidence for AGN activity in ~14 percent of 271 AzTEC
SMGs, ~28 percent considering only the two GOODS fields. Through X-ray spectral
modeling and SED fitting using Monte Carlo Markov Chain techniques to
Siebenmorgen et al. (2004) (AGN) and Efstathiou et al. (2000) (starburst)
templates, we find that while star formation dominates the IR emission, with
SFRs ~100-1000 M_sun/yr, the X-ray emission for most sources is almost
exclusively from obscured AGNs, with column densities in excess of 10^23 cm^-2.
Only for ~6 percent of our sources do we find an X-ray-derived SFR consistent
with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a
prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR,
preventing significant contribution from the AGN template. Our SED modeling
further shows that the AGN and starburst templates typically lack the required
1.1 mm emission necessary to match observations, arguing for an extended, cool
dust component. The cross correlation function between the full samples of
X-ray sources and SMGs in these fields does not indicate a strong correlation
between the two populations at large scales, suggesting that SMGs and AGNs do
not necessarily trace the same underlying large scale structure. Combined with
the remaining X-ray-dim SMGs, this suggests that sub-mm bright sources may
evolve along multiple tracks, with X-ray-detected SMGs representing
transitionary objects between periods of high star formation and AGN activity
while X-ray-faint SMGs represent a brief starburst phase of more normal
galaxies.
We present a large-scale study of the X-ray properties and near-IR-to-radio
SEDs of submillimetre galaxies (SMGs) detected at 1.1mm with the AzTEC
instrument across a ~1.2 square degree area of the sky. Combining deep 2-4 Ms
Chandra data with Spitzer IRAC/MIPS and VLA data within the GOODS-N/S and
COSMOS fields, we find evidence for AGN activity in ~14 percent of 271 AzTEC
SMGs, ~28 percent considering only the two GOODS fields. Through X-ray spectral
modeling and SED fitting using Monte Carlo Markov Chain techniques to
Siebenmorgen et al. (2004) (AGN) and Efstathiou et al. (2000) (starburst)
templates, we find that while star formation dominates the IR emission, with
SFRs ~100-1000 M_sun/yr, the X-ray emission for most sources is almost
exclusively from obscured AGNs, with column densities in excess of 10^23 cm^-2.
Only for ~6 percent of our sources do we find an X-ray-derived SFR consistent
with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a
prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR,
preventing significant contribution from the AGN template. Our SED modeling
further shows that the AGN and starburst templates typically lack the required
1.1 mm emission necessary to match observations, arguing for an extended, cool
dust component. The cross correlation function between the full samples of
X-ray sources and SMGs in these fields does not indicate a strong correlation
between the two populations at large scales, suggesting that SMGs and AGNs do
not necessarily trace the same underlying large scale structure. Combined with
the remaining X-ray-dim SMGs, this suggests that sub-mm bright sources may
evolve along multiple tracks, with X-ray-detected SMGs representing
transitionary objects between periods of high star formation and AGN activity
while X-ray-faint SMGs represent a brief starburst phase of more normal
galaxies.
Nuclear Infrared Spectral Energy Distribution of Type II Active Galactic Nuclei. (arXiv:1301.7000v1 [astro-ph.CO])
Nuclear Infrared Spectral Energy Distribution of Type II Active Galactic Nuclei. (arXiv:1301.7000v1 [astro-ph.CO]):
We present near and mid--IR observations of a sample of Seyfert II galaxies
drawn from the $12\mu$m Galaxy Sample. The sample was observed in the J, H, K,
L, M and N bands. Galaxy Surface Brightness Profiles are modeled using nuclear,
bulge, bar (when necessary) and disk components. To check the reliability of
our findings the procedure was tested using {\em Spitzer\/} observations of
M\,31. Nuclear Spectral Energy Distributions (SEDs) are determined for 34
objects, and optical spectra are presented for 38, including analysis of their
stellar populations using the STARLIGHT spectral synthesis code. Emission line
diagnostic-diagrams are used to discriminate between genuine AGN and HII
nuclei. Combining our observations with those found in the literature, we have
a total of 40 SEDs. It is found that about 40\%\ of the SEDs are characterized
by an upturn in the near-IR, which we have quantified as a NIR slope $\alpha <
1$ for an SED characterized as $\lambda f_{\lambda} \propto \lambda^{\alpha}$.
Three objects with an HII nucleus and two Seyfert nuclei with strong
contamination from a circumnuclear starburst, also show an upturn. For genuine
AGN this component could be explained as emission from the accretion disk, a
jet, or from a very hot dust component leaking from the central region through
a clumpy obscuring structure. The presence of a very compact nuclear starburst
as the origin for this NIR excess emission is not favored by our spectroscopic
data for these objects.
RKS Note: Issue here is distinguishing true AGN from starbursts or H II regions, which can be done in part in the IR as well as in X-ray bands.
We present near and mid--IR observations of a sample of Seyfert II galaxies
drawn from the $12\mu$m Galaxy Sample. The sample was observed in the J, H, K,
L, M and N bands. Galaxy Surface Brightness Profiles are modeled using nuclear,
bulge, bar (when necessary) and disk components. To check the reliability of
our findings the procedure was tested using {\em Spitzer\/} observations of
M\,31. Nuclear Spectral Energy Distributions (SEDs) are determined for 34
objects, and optical spectra are presented for 38, including analysis of their
stellar populations using the STARLIGHT spectral synthesis code. Emission line
diagnostic-diagrams are used to discriminate between genuine AGN and HII
nuclei. Combining our observations with those found in the literature, we have
a total of 40 SEDs. It is found that about 40\%\ of the SEDs are characterized
by an upturn in the near-IR, which we have quantified as a NIR slope $\alpha <
1$ for an SED characterized as $\lambda f_{\lambda} \propto \lambda^{\alpha}$.
Three objects with an HII nucleus and two Seyfert nuclei with strong
contamination from a circumnuclear starburst, also show an upturn. For genuine
AGN this component could be explained as emission from the accretion disk, a
jet, or from a very hot dust component leaking from the central region through
a clumpy obscuring structure. The presence of a very compact nuclear starburst
as the origin for this NIR excess emission is not favored by our spectroscopic
data for these objects.
RKS Note: Issue here is distinguishing true AGN from starbursts or H II regions, which can be done in part in the IR as well as in X-ray bands.
Monday, February 11, 2013
X-ray Detections of Sub-millimetre Galaxies: Active Galactic Nuclei Versus Starburst Contribution. (arXiv:1302.0842v1 [astro-ph.GA])
X-ray Detections of Sub-millimetre Galaxies: Active Galactic Nuclei Versus Starburst Contribution. (arXiv:1302.0842v1 [astro-ph.GA]):
We present a large-scale study of the X-ray properties and near-IR-to-radio
SEDs of submillimetre galaxies (SMGs) detected at 1.1mm with the AzTEC
instrument across a ~1.2 square degree area of the sky. Combining deep 2-4 Ms
Chandra data with Spitzer IRAC/MIPS and VLA data within the GOODS-N/S and
COSMOS fields, we find evidence for AGN activity in ~14 percent of 271 AzTEC
SMGs, ~28 percent considering only the two GOODS fields. Through X-ray spectral
modeling and SED fitting using Monte Carlo Markov Chain techniques to
Siebenmorgen et al. (2004) (AGN) and Efstathiou et al. (2000) (starburst)
templates, we find that while star formation dominates the IR emission, with
SFRs ~100-1000 M_sun/yr, the X-ray emission for most sources is almost
exclusively from obscured AGNs, with column densities in excess of 10^23 cm^-2.
Only for ~6 percent of our sources do we find an X-ray-derived SFR consistent
with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a
prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR,
preventing significant contribution from the AGN template. Our SED modeling
further shows that the AGN and starburst templates typically lack the required
1.1 mm emission necessary to match observations, arguing for an extended, cool
dust component. The cross correlation function between the full samples of
X-ray sources and SMGs in these fields does not indicate a strong correlation
between the two populations at large scales, suggesting that SMGs and AGNs do
not necessarily trace the same underlying large scale structure. Combined with
the remaining X-ray-dim SMGs, this suggests that sub-mm bright sources may
evolve along multiple tracks, with X-ray-detected SMGs representing
transitionary objects between periods of high star formation and AGN activity
while X-ray-faint SMGs represent a brief starburst phase of more normal
galaxies.
We present a large-scale study of the X-ray properties and near-IR-to-radio
SEDs of submillimetre galaxies (SMGs) detected at 1.1mm with the AzTEC
instrument across a ~1.2 square degree area of the sky. Combining deep 2-4 Ms
Chandra data with Spitzer IRAC/MIPS and VLA data within the GOODS-N/S and
COSMOS fields, we find evidence for AGN activity in ~14 percent of 271 AzTEC
SMGs, ~28 percent considering only the two GOODS fields. Through X-ray spectral
modeling and SED fitting using Monte Carlo Markov Chain techniques to
Siebenmorgen et al. (2004) (AGN) and Efstathiou et al. (2000) (starburst)
templates, we find that while star formation dominates the IR emission, with
SFRs ~100-1000 M_sun/yr, the X-ray emission for most sources is almost
exclusively from obscured AGNs, with column densities in excess of 10^23 cm^-2.
Only for ~6 percent of our sources do we find an X-ray-derived SFR consistent
with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a
prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR,
preventing significant contribution from the AGN template. Our SED modeling
further shows that the AGN and starburst templates typically lack the required
1.1 mm emission necessary to match observations, arguing for an extended, cool
dust component. The cross correlation function between the full samples of
X-ray sources and SMGs in these fields does not indicate a strong correlation
between the two populations at large scales, suggesting that SMGs and AGNs do
not necessarily trace the same underlying large scale structure. Combined with
the remaining X-ray-dim SMGs, this suggests that sub-mm bright sources may
evolve along multiple tracks, with X-ray-detected SMGs representing
transitionary objects between periods of high star formation and AGN activity
while X-ray-faint SMGs represent a brief starburst phase of more normal
galaxies.
Wednesday, January 23, 2013
Local Luminous Infrared Galaxies. III. Co-evolution of Black Hole Growth and Star Formation Activity?. (arXiv:1301.4015v1 [astro-ph.CO])
Local Luminous Infrared Galaxies. III. Co-evolution of Black Hole Growth and Star Formation Activity?. (arXiv:1301.4015v1 [astro-ph.CO]):
Local luminous infrared (IR) galaxies (LIRGs) have both high star formation
rates (SFR) and a high AGN (Seyfert and AGN/starburst composite) incidence.
Therefore, they are ideal candidates to explore the co-evolution of black hole
(BH) growth and star formation (SF) activity, not necessarily associated with
major mergers. Here, we use Spitzer/IRS spectroscopy of a complete
volume-limited sample of local LIRGs (distances of <78Mpc). We estimate typical
BH masses of 3x10^7 M_sun using [NeIII]15.56micron and optical [OIII]5007A gas
velocity dispersions and literature stellar velocity dispersions. We find that
in a large fraction of local LIRGs the current SFR is taking place not only in
the inner nuclear ~1.5kpc region, as estimated from the nuclear 11.3micron PAH
luminosities, but also in the host galaxy. We next use the ratios between the
SFRs and BH accretion rates (BHAR) to study whether the SF activity and BH
growth are contemporaneous in local LIRGs. On average, local LIRGs have SFR to
BHAR ratios higher than those of optically selected Seyferts of similar AGN
luminosities. However, the majority of the IR-bright galaxies in the RSA
Seyfert sample behave like local LIRGs. Moreover, the AGN incidence tends to be
higher in local LIRGs with the lowest SFRs. All this suggests that in local
LIRGs there is a distinct IR-bright star forming phase taking place prior to
the bulk of the current BH growth (i.e., AGN phase). The latter is reflected
first as a composite and then as a Seyfert, and later as a non-LIRG optically
identified Seyfert nucleus with moderate SF in its host galaxy.
Local luminous infrared (IR) galaxies (LIRGs) have both high star formation
rates (SFR) and a high AGN (Seyfert and AGN/starburst composite) incidence.
Therefore, they are ideal candidates to explore the co-evolution of black hole
(BH) growth and star formation (SF) activity, not necessarily associated with
major mergers. Here, we use Spitzer/IRS spectroscopy of a complete
volume-limited sample of local LIRGs (distances of <78Mpc). We estimate typical
BH masses of 3x10^7 M_sun using [NeIII]15.56micron and optical [OIII]5007A gas
velocity dispersions and literature stellar velocity dispersions. We find that
in a large fraction of local LIRGs the current SFR is taking place not only in
the inner nuclear ~1.5kpc region, as estimated from the nuclear 11.3micron PAH
luminosities, but also in the host galaxy. We next use the ratios between the
SFRs and BH accretion rates (BHAR) to study whether the SF activity and BH
growth are contemporaneous in local LIRGs. On average, local LIRGs have SFR to
BHAR ratios higher than those of optically selected Seyferts of similar AGN
luminosities. However, the majority of the IR-bright galaxies in the RSA
Seyfert sample behave like local LIRGs. Moreover, the AGN incidence tends to be
higher in local LIRGs with the lowest SFRs. All this suggests that in local
LIRGs there is a distinct IR-bright star forming phase taking place prior to
the bulk of the current BH growth (i.e., AGN phase). The latter is reflected
first as a composite and then as a Seyfert, and later as a non-LIRG optically
identified Seyfert nucleus with moderate SF in its host galaxy.
Evolution of M82-like starburst winds revisited: 3D radiative cooling hydrodynamical simulations. (arXiv:1301.5005v1 [astro-ph.CO])
Evolution of M82-like starburst winds revisited: 3D radiative cooling hydrodynamical simulations. (arXiv:1301.5005v1 [astro-ph.CO]):
In this study we present three-dimensional radiative cooling hydrodynamical
simulations of galactic winds generated particularly in M82-like starburst
galaxies. We have considered intermittent winds induced by SNe explosions
within super star clusters randomly distributed in the central region of the
galaxy and were able to reproduce the observed M82 wind conditions with its
complex morphological outflow structure. We have found that the environmental
conditions in the disk in nearly recent past are crucial to determine whether
the wind will develop a large scale rich filamentary structure, as in M82 wind,
or not. Also, the numerical evolution of the SN ejecta have allowed us to
obtain the abundance distribution over the first 3 kpc extension of the wind
and we have found that the SNe explosions change significantly the metallicity
only of the hot, low-density wind component. Moreover, we have found that the
SN-driven wind transports to outside the disk large amounts of energy, momentum
and gas, but the more massive high-density component reaches only intermediate
altitudes smaller than 1.5 kpc. Therefore, no significant amounts of gas mass
are lost to the IGM and the mass evolution of the galaxy is not much affected
by the starburst events occurring in the nuclear region.
In this study we present three-dimensional radiative cooling hydrodynamical
simulations of galactic winds generated particularly in M82-like starburst
galaxies. We have considered intermittent winds induced by SNe explosions
within super star clusters randomly distributed in the central region of the
galaxy and were able to reproduce the observed M82 wind conditions with its
complex morphological outflow structure. We have found that the environmental
conditions in the disk in nearly recent past are crucial to determine whether
the wind will develop a large scale rich filamentary structure, as in M82 wind,
or not. Also, the numerical evolution of the SN ejecta have allowed us to
obtain the abundance distribution over the first 3 kpc extension of the wind
and we have found that the SNe explosions change significantly the metallicity
only of the hot, low-density wind component. Moreover, we have found that the
SN-driven wind transports to outside the disk large amounts of energy, momentum
and gas, but the more massive high-density component reaches only intermediate
altitudes smaller than 1.5 kpc. Therefore, no significant amounts of gas mass
are lost to the IGM and the mass evolution of the galaxy is not much affected
by the starburst events occurring in the nuclear region.
Sunday, January 20, 2013
Spatially resolved star formation image and the ULX population in NGC2207/IC2163. (arXiv:1301.4084v1 [astro-ph.HE])
Spatially resolved star formation image and the ULX population in NGC2207/IC2163. (arXiv:1301.4084v1 [astro-ph.HE]):
The colliding galaxy pair NGC 2207/IC 2163, at a distance of ~39 Mpc, was
observed with Chandra, and an analysis reveals 22 well resolved, luminous X-ray
sources. Most of these are ultraluminous X-ray sources (ULXs) with Lx>1e+39
erg/s. The number of ULXs is comparable with the largest numbers of ULXs per
unit mass in any galaxy yet reported. In this paper we report on these sources,
and quantify how their locations correlate with the local star formation rates
seen in spatially-resolved star formation rate density images that we have
constructed using combinations of Galex FUV and Spitzer 24{\mu}m images. We
show that the numbers of ULXs are strongly correlated with the local star
formation rate densities surrounding the sources, but that the luminosities of
these sources are not strongly correlated with star formation rate density.
The colliding galaxy pair NGC 2207/IC 2163, at a distance of ~39 Mpc, was
observed with Chandra, and an analysis reveals 22 well resolved, luminous X-ray
sources. Most of these are ultraluminous X-ray sources (ULXs) with Lx>1e+39
erg/s. The number of ULXs is comparable with the largest numbers of ULXs per
unit mass in any galaxy yet reported. In this paper we report on these sources,
and quantify how their locations correlate with the local star formation rates
seen in spatially-resolved star formation rate density images that we have
constructed using combinations of Galex FUV and Spitzer 24{\mu}m images. We
show that the numbers of ULXs are strongly correlated with the local star
formation rate densities surrounding the sources, but that the luminosities of
these sources are not strongly correlated with star formation rate density.
Far-Infrared and submillimeter properties of SDSS galaxies in the Herschel ATLAS science demonstration phase field. (arXiv:1301.4001v1 [astro-ph.CO])
Far-Infrared and submillimeter properties of SDSS galaxies in the Herschel ATLAS science demonstration phase field. (arXiv:1301.4001v1 [astro-ph.CO]):
Using the Herschel ATLAS science demonstration phase data crossidentified
with SDSS DR7 spectra, we select 297 galaxies with F250{\mu}m > 5{\sigma}. The
sample galaxies are classified into five morphological types, and more than 40%
of the galaxies are peculiar/compact galaxies. The peculiar galaxies show
higher far-infrared/submillimeter luminosity-to-mass ratios than the other
types. We perform and analyze the correlations of far-infrared/submillimeter
and H{\alpha} luminosities for different morphological types and different
spectral types. The Spearman rank coefficient decreases and the scatter
increases with the wavelength increasing from 100 {\mu}m to 500 {\mu}m. We
conclude that a single Herschel SPIRE band is not good for tracing star
formation activities in galaxies. AGNs contribute less to the
far-infrared/submillimeter luminosities and do not show a difference from
star-forming galaxies. However, the earlier type galaxies present significant
deviations from the best fit of star-forming galaxies.
Using the Herschel ATLAS science demonstration phase data crossidentified
with SDSS DR7 spectra, we select 297 galaxies with F250{\mu}m > 5{\sigma}. The
sample galaxies are classified into five morphological types, and more than 40%
of the galaxies are peculiar/compact galaxies. The peculiar galaxies show
higher far-infrared/submillimeter luminosity-to-mass ratios than the other
types. We perform and analyze the correlations of far-infrared/submillimeter
and H{\alpha} luminosities for different morphological types and different
spectral types. The Spearman rank coefficient decreases and the scatter
increases with the wavelength increasing from 100 {\mu}m to 500 {\mu}m. We
conclude that a single Herschel SPIRE band is not good for tracing star
formation activities in galaxies. AGNs contribute less to the
far-infrared/submillimeter luminosities and do not show a difference from
star-forming galaxies. However, the earlier type galaxies present significant
deviations from the best fit of star-forming galaxies.
Wednesday, December 19, 2012
A Joint Model of the X-ray And Infrared Extragalactic Backgrounds: I. Model Construction And First Results. (arXiv:1212.3642v1 [astro-ph.CO])
A Joint Model of the X-ray And Infrared Extragalactic Backgrounds: I. Model Construction And First Results. (arXiv:1212.3642v1 [astro-ph.CO]):
We present an extragalactic population model of the cosmic background light
to interpret the rich high-quality survey data in the X-ray and IR bands. The
model incorporates star-formation and supermassive black hole (SMBH) accretion
in a co-evolution scenario to fit simultaneously 617 data points of number
counts, redshift distributions and local luminosity functions (LFs) with 19
free parameters. The model has four main components, the total IR LF, the SMBH
accretion energy fraction in the IR band, the star-formation SED and the
unobscured SMBH SED extinguished with a HI column density distribution. As a
result of the observational uncertainties about the star-formation and SMBH
SEDs, we present several variants of the model. The best-fit reduced chi^2
reaches as small as 2.7-2.9 of which a significant amount (>0.8) is contributed
by cosmic variances or caveats associated with data. Compared to previous
models, the unique result of this model is to constrain the SMBH energy
fraction in the IR band that is found to increase with the IR luminosity but
decrease with redshift up to z ~ 1.5; this result is separately verified using
aromatic feature equivalent width data. The joint modelling of X-ray and mid-IR
data allows for improved constraints on the obscured AGN, especially the
Compton-thick AGN population. All variants of the model require that
Compton-thick AGN fractions decrease with the SMBH luminosity but increase with
redshift while the type-1 AGN fraction has the reverse trend.
We present an extragalactic population model of the cosmic background light
to interpret the rich high-quality survey data in the X-ray and IR bands. The
model incorporates star-formation and supermassive black hole (SMBH) accretion
in a co-evolution scenario to fit simultaneously 617 data points of number
counts, redshift distributions and local luminosity functions (LFs) with 19
free parameters. The model has four main components, the total IR LF, the SMBH
accretion energy fraction in the IR band, the star-formation SED and the
unobscured SMBH SED extinguished with a HI column density distribution. As a
result of the observational uncertainties about the star-formation and SMBH
SEDs, we present several variants of the model. The best-fit reduced chi^2
reaches as small as 2.7-2.9 of which a significant amount (>0.8) is contributed
by cosmic variances or caveats associated with data. Compared to previous
models, the unique result of this model is to constrain the SMBH energy
fraction in the IR band that is found to increase with the IR luminosity but
decrease with redshift up to z ~ 1.5; this result is separately verified using
aromatic feature equivalent width data. The joint modelling of X-ray and mid-IR
data allows for improved constraints on the obscured AGN, especially the
Compton-thick AGN population. All variants of the model require that
Compton-thick AGN fractions decrease with the SMBH luminosity but increase with
redshift while the type-1 AGN fraction has the reverse trend.
Monday, December 17, 2012
An X-ray study of the galactic-scale starburst-driven outflow in NGC 253. (arXiv:1212.1904v1 [astro-ph.CO])
An X-ray study of the galactic-scale starburst-driven outflow in NGC 253. (arXiv:1212.1904v1 [astro-ph.CO]):
X-ray properties of hot interstellar gas in a starburst galaxy NGC 253 were
investigated to gain a further understanding of starburst-driven outflow
activity by XMM-Newton and Suzaku. Spectroscopic analysis for three regions of
the galaxy characterized by multiwavelength observations was conducted. The hot
gas was represented by two thin thermal plasmas with temperatures of kT ~0.2
and ~0.6 keV. Abundance ratios i.e., O/Fe, Ne/Fe, Mg/Fe and Si/Fe, are
consistent between three regions, which suggests the common origin of the hot
gas. The abundance patterns are consistent with those of type II supernova
ejecta, indicating that the starburst activity in the central region provides
metals toward the halo through a galactic-scale starburst-driven outflow. The
energetics also can support this indication on condition that 0.01-50
{\eta}^0.5 % of the total emission in the nuclear region has flowed to the halo
region. To constrain the dynamics of hot interstellar gas, surface brightness
and hardness ratio profiles which trace the density and temperature were
extracted. Assuming a simple polytropic equation of state of gas,
T{\rho}^(1-{\gamma}) = const, we constrained the physical condition. {\gamma}
is consistent with 5/3 at the hot disk and T is constant ({\gamma} = 1) in the
halo. It is suggested that the hot gas expands adiabatically from the central
region towards the halo region while it moves as free expansion from the inner
part of the halo towards the outer part of the halo as the outflow. We
constrained the outflow velocity to be >100 km s^-1 from the observed
temperature gradient in the halo. In comparison with the escape velocity of
~220 km s^-1 for NGC 253, it is indicated that the hot interstellar gas can
escape from the gravitational potential of NGC 253 by combining the outflow
velocity and the thermal velocity.
X-ray properties of hot interstellar gas in a starburst galaxy NGC 253 were
investigated to gain a further understanding of starburst-driven outflow
activity by XMM-Newton and Suzaku. Spectroscopic analysis for three regions of
the galaxy characterized by multiwavelength observations was conducted. The hot
gas was represented by two thin thermal plasmas with temperatures of kT ~0.2
and ~0.6 keV. Abundance ratios i.e., O/Fe, Ne/Fe, Mg/Fe and Si/Fe, are
consistent between three regions, which suggests the common origin of the hot
gas. The abundance patterns are consistent with those of type II supernova
ejecta, indicating that the starburst activity in the central region provides
metals toward the halo through a galactic-scale starburst-driven outflow. The
energetics also can support this indication on condition that 0.01-50
{\eta}^0.5 % of the total emission in the nuclear region has flowed to the halo
region. To constrain the dynamics of hot interstellar gas, surface brightness
and hardness ratio profiles which trace the density and temperature were
extracted. Assuming a simple polytropic equation of state of gas,
T{\rho}^(1-{\gamma}) = const, we constrained the physical condition. {\gamma}
is consistent with 5/3 at the hot disk and T is constant ({\gamma} = 1) in the
halo. It is suggested that the hot gas expands adiabatically from the central
region towards the halo region while it moves as free expansion from the inner
part of the halo towards the outer part of the halo as the outflow. We
constrained the outflow velocity to be >100 km s^-1 from the observed
temperature gradient in the halo. In comparison with the escape velocity of
~220 km s^-1 for NGC 253, it is indicated that the hot interstellar gas can
escape from the gravitational potential of NGC 253 by combining the outflow
velocity and the thermal velocity.
Wednesday, December 12, 2012
Testing Diagnostics of Nuclear Activity and Star Formation in Galaxies at z>1. (arXiv:1212.2218v1 [astro-ph.CO])
Testing Diagnostics of Nuclear Activity and Star Formation in Galaxies at z>1. (arXiv:1212.2218v1 [astro-ph.CO]):
We present some of the first science data with the new Keck/MOSFIRE
instrument to test the effectiveness of different AGN/SF diagnostics at z~1.5.
MOSFIRE spectra were obtained in three H-band multi-slit masks in the GOODS-S
field, resulting in two hour exposures of 36 emission-line galaxies. We compare
X-ray data with the traditional "BPT" line ratio diagnostics and the
alternative mass-excitation and color-excitation diagrams, combining new
MOSFIRE infrared data with previous HST/WFC3 infrared spectra (from the 3D-HST
survey) and multiwavelength photometry. We demonstrate that a high [OIII]/\Hb
ratio is insufficient as an AGN indicator at z>1. For the four X-ray detected
galaxies, the classic BPT diagnostic ([OIII]/Hb vs. [NII]/Ha and [SII]/Ha)
remains consistent with X-ray AGN/SF classification. The X-ray data also
suggest that "composite" galaxies (with intermediate AGN/SF classification)
host bona-fide AGNs. Nearly 2/3 of the z~1.5 emission-line galaxies have
nuclear activity detected by either X-rays or the BPT diagnostic. Compared to
the X-ray and BPT classifications, the mass-excitation method remains effective
at z>1, but we show that the color-excitation method requires a new calibration
to successfully identify AGNs at these redshifts.
We present some of the first science data with the new Keck/MOSFIRE
instrument to test the effectiveness of different AGN/SF diagnostics at z~1.5.
MOSFIRE spectra were obtained in three H-band multi-slit masks in the GOODS-S
field, resulting in two hour exposures of 36 emission-line galaxies. We compare
X-ray data with the traditional "BPT" line ratio diagnostics and the
alternative mass-excitation and color-excitation diagrams, combining new
MOSFIRE infrared data with previous HST/WFC3 infrared spectra (from the 3D-HST
survey) and multiwavelength photometry. We demonstrate that a high [OIII]/\Hb
ratio is insufficient as an AGN indicator at z>1. For the four X-ray detected
galaxies, the classic BPT diagnostic ([OIII]/Hb vs. [NII]/Ha and [SII]/Ha)
remains consistent with X-ray AGN/SF classification. The X-ray data also
suggest that "composite" galaxies (with intermediate AGN/SF classification)
host bona-fide AGNs. Nearly 2/3 of the z~1.5 emission-line galaxies have
nuclear activity detected by either X-rays or the BPT diagnostic. Compared to
the X-ray and BPT classifications, the mass-excitation method remains effective
at z>1, but we show that the color-excitation method requires a new calibration
to successfully identify AGNs at these redshifts.
Thursday, October 25, 2012
Modeling Mid-Infrared Diagnostics of Obscured Quasars and Starbursts. (arXiv:1210.6347v1 [astro-ph.CO])
Modeling Mid-Infrared Diagnostics of Obscured Quasars and Starbursts. (arXiv:1210.6347v1 [astro-ph.CO]):
We analyze the link between active galactic nuclei (AGN) and mid-infrared
flux using dust radiative transfer calculations of starbursts realized in
hydrodynamical simulations. Focusing on the effect of galaxy dust, we evaluate
diagnostics commonly used to disentangle AGN and star formation in
ultraluminous infrared galaxies (ULIRGs). We examine these quantities as a
function of time, viewing angle, dust model, AGN spectrum, and AGN strength in
merger simulations meant to bracket the properties of ULIRGs. Our more obscured
starburst begins SF-dominated with significant PAH emission, and ends with a
~10^9 year period of red near-IR colors. At coalescence, when the AGN is most
luminous, dust obscures the near-infrared AGN signature, reduces the relative
emission from polycyclic aromatic hydrocarbons (PAHs), and enhances the 9.7
micron absorption by silicate grains. Although generally consistent with
previous interpretations, our results imply none of these indicators can
unambiguously estimate the AGN luminosity fraction in all cases. Some identify
relatively unobscured AGN where the direct torus emission is observed, while
others indicate more highly obscured AGN. We show that a combination of the
extinction feature at 9.7 microns, the PAH strength, and a near-infrared slope
can simultaneously constrain the AGN fraction and dust grain distribution for a
wide range of obscuration. We find that this procedure, accessible to the James
Webb Space Telescope, may estimate the AGN power as tightly as the hard X-ray
flux alone, thereby providing a valuable future cross-check and constraint for
large samples of distant ULIRGs.
We analyze the link between active galactic nuclei (AGN) and mid-infrared
flux using dust radiative transfer calculations of starbursts realized in
hydrodynamical simulations. Focusing on the effect of galaxy dust, we evaluate
diagnostics commonly used to disentangle AGN and star formation in
ultraluminous infrared galaxies (ULIRGs). We examine these quantities as a
function of time, viewing angle, dust model, AGN spectrum, and AGN strength in
merger simulations meant to bracket the properties of ULIRGs. Our more obscured
starburst begins SF-dominated with significant PAH emission, and ends with a
~10^9 year period of red near-IR colors. At coalescence, when the AGN is most
luminous, dust obscures the near-infrared AGN signature, reduces the relative
emission from polycyclic aromatic hydrocarbons (PAHs), and enhances the 9.7
micron absorption by silicate grains. Although generally consistent with
previous interpretations, our results imply none of these indicators can
unambiguously estimate the AGN luminosity fraction in all cases. Some identify
relatively unobscured AGN where the direct torus emission is observed, while
others indicate more highly obscured AGN. We show that a combination of the
extinction feature at 9.7 microns, the PAH strength, and a near-infrared slope
can simultaneously constrain the AGN fraction and dust grain distribution for a
wide range of obscuration. We find that this procedure, accessible to the James
Webb Space Telescope, may estimate the AGN power as tightly as the hard X-ray
flux alone, thereby providing a valuable future cross-check and constraint for
large samples of distant ULIRGs.
Thursday, October 18, 2012
X-ray stacking of Lyman break galaxies in the 4\,Ms CDF-S - X-ray luminosities and star formation rates across cosmic time. (arXiv:1210.4188v1 [astro-ph.CO])
X-ray stacking of Lyman break galaxies in the 4\,Ms CDF-S - X-ray luminosities and star formation rates across cosmic time. (arXiv:1210.4188v1 [astro-ph.CO]):
Lyman Break Galaxies (LBGs) are widely thought to be prototypical young
galaxies in the early universe, particularly representative of those undergoing
massive events of star formation. Therefore, LBGs should produce significant
amounts of X-ray emission. We aim to trace the X-ray luminosity of Lyman Break
Galaxies across cosmic time and from that derive constraints on their star
formation history. We utilize the newly released 4 Ms mosaic obtained with the
Chandra X-ray Observatory, the deepest X-ray image to date, alongside with the
superb spectroscopic data sets available in the CDF-S survey region to
construct large but nearly uncontaminated samples of LBGs across a wide range
of redshift (0.5 < z < 4.5) which can be used as input samples for stacking
experiments. This approach allows us to trace the X-ray emission of Lyman Break
Galaxies to even lower, previously unreachable, flux density limits (~10^-18 mW
m^-2) and therefore to larger redshifts. We reliably detect soft-band X-ray
emission from all our input redshift bins except for the highest redshift (z~4)
one. From that we derive rest-frame 2-10 keV luminosities and infer star
formation rates and stellar masses. We find that star formation in LBGs peaks
at a redshift of z_peak~3.5 and then decreases quickly. We also see a
characteristic peak in the specific star formation rate (sSFR=SFR/M_*) at this
redshift. Furthermore, we calculate the contribution of LBGs to the total
cosmic star formation rate density (SFRD) and find that the contribution of
LBGs is negligible. Therefore, we conclude that most of the star formation in
the early universe takes place in lower luminosity galaxies as suggested by
hierarchical structure formation models.
Lyman Break Galaxies (LBGs) are widely thought to be prototypical young
galaxies in the early universe, particularly representative of those undergoing
massive events of star formation. Therefore, LBGs should produce significant
amounts of X-ray emission. We aim to trace the X-ray luminosity of Lyman Break
Galaxies across cosmic time and from that derive constraints on their star
formation history. We utilize the newly released 4 Ms mosaic obtained with the
Chandra X-ray Observatory, the deepest X-ray image to date, alongside with the
superb spectroscopic data sets available in the CDF-S survey region to
construct large but nearly uncontaminated samples of LBGs across a wide range
of redshift (0.5 < z < 4.5) which can be used as input samples for stacking
experiments. This approach allows us to trace the X-ray emission of Lyman Break
Galaxies to even lower, previously unreachable, flux density limits (~10^-18 mW
m^-2) and therefore to larger redshifts. We reliably detect soft-band X-ray
emission from all our input redshift bins except for the highest redshift (z~4)
one. From that we derive rest-frame 2-10 keV luminosities and infer star
formation rates and stellar masses. We find that star formation in LBGs peaks
at a redshift of z_peak~3.5 and then decreases quickly. We also see a
characteristic peak in the specific star formation rate (sSFR=SFR/M_*) at this
redshift. Furthermore, we calculate the contribution of LBGs to the total
cosmic star formation rate density (SFRD) and find that the contribution of
LBGs is negligible. Therefore, we conclude that most of the star formation in
the early universe takes place in lower luminosity galaxies as suggested by
hierarchical structure formation models.
Monday, October 15, 2012
The X-ray Star Formation Story as Told by Lyman Break Galaxies in the 4 Ms CDF-S. (arXiv:1210.3357v1 [astro-ph.CO])
The X-ray Star Formation Story as Told by Lyman Break Galaxies in the 4 Ms CDF-S. (arXiv:1210.3357v1 [astro-ph.CO]):
We present results from deep X-ray stacking of >4000 high redshift galaxies
from z~1 to 8 using the 4 Ms Chandra Deep Field South (CDF-S) data, the deepest
X-ray survey of the extragalactic sky to date. The galaxy samples were selected
using the Lyman break technique based primarily on recent HST ACS and WFC3
observations. Based on such high specific star formation rates (sSFRs): log
SFR/M* > -8.7, we expect that the observed properties of these LBGs are
dominated by young stellar populations. The X-ray emission in LBGs, eliminating
individually detected X-ray sources (potential AGN), is expected to be powered
by X-ray binaries and hot gas. We find, for the first time, evidence of
evolution in the X-ray/SFR relation. Based on X-ray stacking analyses for z<4
LBGs (covering ~90% of the Universe's history), we find that the 2-10 keV X-ray
luminosity evolves weakly with redshift (z) and SFR as log LX = 0.93 log (1+z)
+ 0.65 log SFR + 39.80. By comparing our observations with sophisticated X-ray
binary population synthesis models, we interpret that the redshift evolution of
LX/SFR is driven by metallicity evolution in HMXBs, likely the dominant
population in these high sSFR galaxies. We also compare these models with our
observations of X-ray luminosity density (total 2-10 keV luminosity per Mpc^3)
and find excellent agreement. While there are no significant stacked detections
at z>5, we use our upper limits from 5<z<8 LBGs to constrain the SMBH accretion
history of the Universe around the epoch of reionization.
We present results from deep X-ray stacking of >4000 high redshift galaxies
from z~1 to 8 using the 4 Ms Chandra Deep Field South (CDF-S) data, the deepest
X-ray survey of the extragalactic sky to date. The galaxy samples were selected
using the Lyman break technique based primarily on recent HST ACS and WFC3
observations. Based on such high specific star formation rates (sSFRs): log
SFR/M* > -8.7, we expect that the observed properties of these LBGs are
dominated by young stellar populations. The X-ray emission in LBGs, eliminating
individually detected X-ray sources (potential AGN), is expected to be powered
by X-ray binaries and hot gas. We find, for the first time, evidence of
evolution in the X-ray/SFR relation. Based on X-ray stacking analyses for z<4
LBGs (covering ~90% of the Universe's history), we find that the 2-10 keV X-ray
luminosity evolves weakly with redshift (z) and SFR as log LX = 0.93 log (1+z)
+ 0.65 log SFR + 39.80. By comparing our observations with sophisticated X-ray
binary population synthesis models, we interpret that the redshift evolution of
LX/SFR is driven by metallicity evolution in HMXBs, likely the dominant
population in these high sSFR galaxies. We also compare these models with our
observations of X-ray luminosity density (total 2-10 keV luminosity per Mpc^3)
and find excellent agreement. While there are no significant stacked detections
at z>5, we use our upper limits from 5<z<8 LBGs to constrain the SMBH accretion
history of the Universe around the epoch of reionization.
Tuesday, September 18, 2012
No clear submillimetre signature of suppressed star formation amongst X-ray luminous AGNs. (arXiv:1209.3016v1 [astro-ph.CO])
No clear submillimetre signature of suppressed star formation amongst X-ray luminous AGNs. (arXiv:1209.3016v1 [astro-ph.CO]):
Many theoretical models require powerful active galactic nuclei (AGNs) to
suppress star formation in distant galaxies and reproduce the observed
properties of today's massive galaxies. A recent study based on Herschel-SPIRE
submillimetre observations claimed to provide direct support for this picture,
reporting a significant decrease in the mean star-formation rates (SFRs) of the
most luminous AGNs (Lx>10^44 erg/s) at z=1-3 in the Chandra Deep Field-North
(CDF-N). In this letter we extend these results using Herschel-SPIRE 250um data
in the COSMOS and CDF-S fields to achieve an order of magnitude improvement in
the number of sources at Lx>10^44 erg/s. On the basis of our analyses, we find
no strong evidence for suppressed star formation in Lx>10^44 erg/s AGNs at
z=1-3. The mean SFRs of the AGNs are constant over the broad X-ray luminosity
range of Lx~10^43-10^45 erg/s (with mean SFRs consistent with typical
star-forming galaxies at z~2; <SFRs>~100-200 Msol/yr). We suggest that the
previous CDF-N results were likely due to low number statistics. We discuss our
results in the context of current theoretical models and suggest that it will
be challenging to see the signature of suppressed star formation simply on the
basis of an X-ray luminosity threshold.
Many theoretical models require powerful active galactic nuclei (AGNs) to
suppress star formation in distant galaxies and reproduce the observed
properties of today's massive galaxies. A recent study based on Herschel-SPIRE
submillimetre observations claimed to provide direct support for this picture,
reporting a significant decrease in the mean star-formation rates (SFRs) of the
most luminous AGNs (Lx>10^44 erg/s) at z=1-3 in the Chandra Deep Field-North
(CDF-N). In this letter we extend these results using Herschel-SPIRE 250um data
in the COSMOS and CDF-S fields to achieve an order of magnitude improvement in
the number of sources at Lx>10^44 erg/s. On the basis of our analyses, we find
no strong evidence for suppressed star formation in Lx>10^44 erg/s AGNs at
z=1-3. The mean SFRs of the AGNs are constant over the broad X-ray luminosity
range of Lx~10^43-10^45 erg/s (with mean SFRs consistent with typical
star-forming galaxies at z~2; <SFRs>~100-200 Msol/yr). We suggest that the
previous CDF-N results were likely due to low number statistics. We discuss our
results in the context of current theoretical models and suggest that it will
be challenging to see the signature of suppressed star formation simply on the
basis of an X-ray luminosity threshold.
Friday, September 14, 2012
Accreting SMBHs in the COSMOS field and the connection to their host galaxies. (arXiv:1209.1640v1 [astro-ph.CO])
Accreting SMBHs in the COSMOS field and the connection to their host galaxies. (arXiv:1209.1640v1 [astro-ph.CO]):
Using the wide multi-band photometry available in the COSMOS field we explore
the host galaxy properties of a large sample of Active Galactic Nuclei (AGN)
obtained by combining X-ray and optical spectroscopic selections. Based on a
careful study of their Spectral Energy Distribution (SED), which has been
parametrized using a 2-component (AGN+galaxy) model fit, we derived
dust-corrected rest-frame magnitudes, colors, stellar masses and star formation
rates (SFRs). We find that AGN hosts span a large range of stellar masses and
SFRs. No color-bimodality is seen at any redshift in the AGN hosts, which are
found to be mainly massive, red galaxies. Once accounting for the color-mass
degeneracy in well defined mass-matched samples, we find a residual marginal
enhancement of AGN incidence in redder galaxies with lower specific star
formation rates, and we argue that this result might emerge because of our
ability to properly account for AGN light contamination and dust extinction.
Interestingly, we find that the probability for a galaxy to host a black hole
growing at any given "specific accretion rate" (i.e. the ratio of X-ray
luminosity to the host stellar mass) is almost independent of the host galaxy
mass, while it decreases as a power-law with Lx/M. By analyzing the
normalization of such probability distribution, we show how the incidence of
AGN increases with redshift as rapidly as (1+z)^4, in close resemblance with
the overall evolution of the specific star formation rate of the entire galaxy
population. Although AGN activity and star formation in galaxies do appear to
have a common triggering mechanism, at least in a statistical sense, within the
COSMOS sample we do not find strong evidence of any 'smoking gun' signaling
powerful AGN influence on the star-forming properties of their hosts galaxies.
Using the wide multi-band photometry available in the COSMOS field we explore
the host galaxy properties of a large sample of Active Galactic Nuclei (AGN)
obtained by combining X-ray and optical spectroscopic selections. Based on a
careful study of their Spectral Energy Distribution (SED), which has been
parametrized using a 2-component (AGN+galaxy) model fit, we derived
dust-corrected rest-frame magnitudes, colors, stellar masses and star formation
rates (SFRs). We find that AGN hosts span a large range of stellar masses and
SFRs. No color-bimodality is seen at any redshift in the AGN hosts, which are
found to be mainly massive, red galaxies. Once accounting for the color-mass
degeneracy in well defined mass-matched samples, we find a residual marginal
enhancement of AGN incidence in redder galaxies with lower specific star
formation rates, and we argue that this result might emerge because of our
ability to properly account for AGN light contamination and dust extinction.
Interestingly, we find that the probability for a galaxy to host a black hole
growing at any given "specific accretion rate" (i.e. the ratio of X-ray
luminosity to the host stellar mass) is almost independent of the host galaxy
mass, while it decreases as a power-law with Lx/M. By analyzing the
normalization of such probability distribution, we show how the incidence of
AGN increases with redshift as rapidly as (1+z)^4, in close resemblance with
the overall evolution of the specific star formation rate of the entire galaxy
population. Although AGN activity and star formation in galaxies do appear to
have a common triggering mechanism, at least in a statistical sense, within the
COSMOS sample we do not find strong evidence of any 'smoking gun' signaling
powerful AGN influence on the star-forming properties of their hosts galaxies.
Monday, September 10, 2012
AGN feedback and triggering of star formation in galaxies. (arXiv:1209.1480v1 [astro-ph.GA])
AGN feedback and triggering of star formation in galaxies. (arXiv:1209.1480v1 [astro-ph.GA]):
Feedback from the central black hole in active galactic nuclei (AGN) may be
responsible for establishing the observed MBH-sigma relation and limiting the
bulge stellar mass of the host galaxy. Here we explore the possibility of AGN
feedback triggering star formation in the host galaxy. We consider a shell of
dusty gas, driven outwards by radiation pressure, and analyse its
escape/trapping condition in the galactic halo for different underlying dark
matter potentials. In the isothermal potential, we obtain that the standard
condition setting the observed MBH-sigma relation is not sufficient to clear
gas out of the entire galaxy; whereas the same condition is formally sufficient
in the case of the Hernquist and Navarro-Frenk-White profiles. The squeezing
and compression of the inhomogeneous interstellar medium during the ejection
process can trigger star formation within the feedback-driven shell. We
estimate the resulting star formation rate and total additional stellar mass.
In this picture, new stars are formed at increasingly larger radii and
successively populate the outer regions of the host galaxy. This characteristic
pattern may be compared with the observed 'inside-out' growth of massive
galaxies.
Feedback from the central black hole in active galactic nuclei (AGN) may be
responsible for establishing the observed MBH-sigma relation and limiting the
bulge stellar mass of the host galaxy. Here we explore the possibility of AGN
feedback triggering star formation in the host galaxy. We consider a shell of
dusty gas, driven outwards by radiation pressure, and analyse its
escape/trapping condition in the galactic halo for different underlying dark
matter potentials. In the isothermal potential, we obtain that the standard
condition setting the observed MBH-sigma relation is not sufficient to clear
gas out of the entire galaxy; whereas the same condition is formally sufficient
in the case of the Hernquist and Navarro-Frenk-White profiles. The squeezing
and compression of the inhomogeneous interstellar medium during the ejection
process can trigger star formation within the feedback-driven shell. We
estimate the resulting star formation rate and total additional stellar mass.
In this picture, new stars are formed at increasingly larger radii and
successively populate the outer regions of the host galaxy. This characteristic
pattern may be compared with the observed 'inside-out' growth of massive
galaxies.
Thursday, September 6, 2012
Plunging fireworks: Why do infalling galaxies light up on the outskirts of clusters?. (arXiv:1209.0972v1 [astro-ph.CO])
Plunging fireworks: Why do infalling galaxies light up on the outskirts of clusters?. (arXiv:1209.0972v1 [astro-ph.CO]):
(abridged)Integrated star formation rate (SFR) and specific star formation
rate (sSFR), derived from the spectroscopic data obtained by SDSS DR4 are used
to show that the star formation activity in galaxies (M_r<=-20.5) found on the
outskirts (1-2r_{200}) of some nearby clusters (0.02<=z<=0.15) is enhanced. By
comparing the mean SFR of galaxies in a sample of clusters with at least one
starburst galaxy (log sSFR>=-10/yr & SFR>10 M_sun/yr) to a sample of clusters
without such galaxies (`comparison' clusters), we find that despite the
expected decline in the mean SFR of galaxies toward the cluster core, the SFR
profile of the two samples is different, such that the galaxies in the
`comparison' clusters show a lower mean SFR at all radius (<=3r_{200}) from the
cluster centre. Such an increase in the SFR of galaxies is more likely to be
seen in dynamically unrelaxed (sigma_v>~500 km/s) clusters. It is also evident
that these unrelaxed clusters are currently being assembled via galaxies
falling in through straight filaments, resulting in high velocity dispersions.
On the other hand, `comparison' clusters are more likely to be fed by
relatively low density filaments. We find that the starburst galaxies on the
periphery of clusters are in an environment of higher local density than other
cluster galaxies at similar radial distances from the cluster centre. We
conclude that a relatively high galaxy density in the infalling regions of
clusters promotes interactions amongst galaxies, leading to momentary bursts of
star formation. Such interactions play a crucial role in exhausting the fuel
for star formation in a galaxy, before it is expelled due to the environmental
processes that are operational in the dense interiors of the cluster.
(abridged)Integrated star formation rate (SFR) and specific star formation
rate (sSFR), derived from the spectroscopic data obtained by SDSS DR4 are used
to show that the star formation activity in galaxies (M_r<=-20.5) found on the
outskirts (1-2r_{200}) of some nearby clusters (0.02<=z<=0.15) is enhanced. By
comparing the mean SFR of galaxies in a sample of clusters with at least one
starburst galaxy (log sSFR>=-10/yr & SFR>10 M_sun/yr) to a sample of clusters
without such galaxies (`comparison' clusters), we find that despite the
expected decline in the mean SFR of galaxies toward the cluster core, the SFR
profile of the two samples is different, such that the galaxies in the
`comparison' clusters show a lower mean SFR at all radius (<=3r_{200}) from the
cluster centre. Such an increase in the SFR of galaxies is more likely to be
seen in dynamically unrelaxed (sigma_v>~500 km/s) clusters. It is also evident
that these unrelaxed clusters are currently being assembled via galaxies
falling in through straight filaments, resulting in high velocity dispersions.
On the other hand, `comparison' clusters are more likely to be fed by
relatively low density filaments. We find that the starburst galaxies on the
periphery of clusters are in an environment of higher local density than other
cluster galaxies at similar radial distances from the cluster centre. We
conclude that a relatively high galaxy density in the infalling regions of
clusters promotes interactions amongst galaxies, leading to momentary bursts of
star formation. Such interactions play a crucial role in exhausting the fuel
for star formation in a galaxy, before it is expelled due to the environmental
processes that are operational in the dense interiors of the cluster.
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