161 research outputs found
Infrared Classification and Luminosities For Dusty AGN and the Most Luminous Quasars
Mid-infrared spectroscopic measurements from the Infrared Spectrometer on
Spitzer (IRS) are given for 125 hard X-ray AGN (14-195 keV) from the Swift
Burst Alert Telescope sample and for 32 AGN with black hole masses from
reverberation mapping. The 9.7 um silicate feature in emission or absorption
defines an infrared AGN classification describing whether AGN are observed
through dust clouds, indicating that 55% of the BAT AGN are observed through
dust. The mid-infrared dust continuum luminosity is shown to be an excellent
indicator of intrinsic AGN luminosity, scaling closely with the hard X-ray
luminosity, log vLv(7.8 um)/L(X) = -0.31 +- 0.35 and independent of
classification determined from silicate emission or absorption. Dust luminosity
scales closely with black hole mass, log vLv(7.8 um) = (37.2 +- 0.5) + 0.87 log
BHM for luminosity in erg per sec and BHM in solar masses. The 100 most
luminous type 1 quasars as measured in vLv(7.8 um) are found by comparing Sloan
Digital Sky Survey optically discovered quasars with photometry at 22 um from
the Wide-Field Infrared Survey Explorer, scaled to rest frame 7.8 um using an
empirical template determined from IRS spectra. The most luminous SDSS/WISE
quasars have the same maximum infrared luminosities for all 1.5 < z < 5,
reaching total infrared luminosity L(IR) = 10^14.4 solar luminosities.
Comparing with Dust Obscured Galaxies from Spitzer and WISE surveys, we find no
evidence of hyperluminous obscured quasars whose maximum infrared luminosities
exceed the maximum infrared luminosities of optically discovered quasars.
Bolometric luminosities L(bol) estimated from rest frame optical or ultraviolet
luminosities are compared to L(IR).Comment: accepted for publication in The Astrophysical Journa
Evolution of the Most Luminous Dusty Galaxies
A summary of mid-infrared continuum luminosities arising from dust is given
for very luminous galaxies, Lir > 10^12 solar luminosities, with 0.005 < z <
3.2 containing active galactic nuclei (AGN), including 115 obscured AGN and 60
unobscured (type 1) AGN. All sources have been observed with the Spitzer
Infrared Spectrograph. Obscured AGN are defined as having optical depth > 0.7
in the 9.7 um silicate absorption feature and unobscured AGN show silicate in
emission. Luminosity vLv(8 um) is found to scale as (1+z)^2.6 to z = 2.8, and
luminosities vLv(8 um) are approximately 3 times greater for the most luminous
unobscured AGN. Total infrared luminosities for the most luminous obscured AGN,
Lir(AGN_obscured) in solar luminosities, scale as log Lir(AGN_obscured) =
12.3+-0.25 + 2.6(+-0.3)log(1+z), and for the most luminous unobscured AGN,
scale as log Lir(AGN1) = 12.6+-0.15 + 2.6(+-0.3)log(1+z), indicating that the
most luminous AGN are about 10 times more luminous than the most luminous
starbursts. Results are consistent with obscured and unobscured AGN having the
same total luminosities with differences arising only from orientation, such
that the obscured AGN are observed through very dusty clouds which extinct
about 50% of the intrinsic luminosity at 8 um. Both obscured and unobscured AGN
should be detected to z ~ 6 by Spitzer surveys with fv(24 um) > 0.3 mJy, even
without luminosity evolution for z > 2.5. By contrast, the most luminous
starbursts cannot be detected for z > 3, even if luminosity evolution continues
beyond z = 2.5.Comment: Includes corrected Figure 3, as publishe
Starburst galaxies
The infrared properties of star-forming galaxies, primarily as determined by the Infrared Astronomy Satellite (IRAS), are compared to X-ray, optical, and radio properties. Luminosity functions are reviewed and combined with those derived from optically discovered samples using 487 Markarian galaxies with redshifts and published IRAS 60 micron fluxes, and 1074 such galaxies in the Center for Astrophysics redshift survey. It is found that the majority of infrared galaxies which could be detected are low luminosity sources already known from the optical samples, but non-infrared surveys have found only a very small fraction of the highest luminosity sources. Distributions of infrared to optical fluxes and available spectra indicate that the majority of IRAS-selected galaxies are starburst galaxies. Having a census of starburst galaxies and associated dust allow severl important global calculations. The source counts are predicted as a function of flux limits for both infrared and radio fluxes. These galaxies are found to be important radio sources at faint flux limits. Taking the integrated flux to z = 3 indicates that such galaxies are a significant component of the diffuse X-ray background, and could be the the dominant component depending on the nature of the X-ray spectra and source evolution
Spitzer IRS Spectra of Optically Faint Infrared Sources with Weak Spectral Features
Spectra have been obtained with the low-resolution modules of the Infrared
Spectrograph (IRS) on the Spitzer Space Telescope (Spitzer) for 58 sources
having f(24 micron) > 0.75 mJy. Sources were chosen from a survey of
8.2 deg within the NOAO Deep Wide-Field Survey region in Bootes (NDWFS)
using the Multiband Imaging Photometer (MIPS) on the Spitzer Space Telescope.
Most sources are optically very faint (I > 24mag). Redshifts have previously
been determined for 34 sources, based primarily on the presence of a deep 9.7
micron silicate absorption feature, with a median z of 2.2. Spectra are
presented for the remaining 24 sources for which we were previously unable to
determine a confident redshift because the IRS spectra show no strong features.
Optical photometry from the NDWFS and infrared photometry with MIPS and the
Infrared Array Camera on the Spitzer Space Telescope (IRAC) are given, with K
photometry from the Keck I telescope for some objects. The sources without
strong spectral features have overall spectral energy distributions (SEDs) and
distributions among optical and infrared fluxes which are similar to those for
the sources with strong absorption features. Nine of the 24 sources are found
to have feasible redshift determinations based on fits of a weak silicate
absorption feature. Results confirm that the "1 mJy" population of 24 micron
Spitzer sources which are optically faint is dominated by dusty sources with
spectroscopic indicators of an obscured AGN rather than a starburst. There
remain 14 of the 58 sources observed in Bootes for which no redshift could be
estimated, and 5 of these sources are invisible at all optical wavelengths.Comment: Accepted by Ap
Observations of Feedback from Radio-Quiet Quasars - II. Kinematics of Ionized Gas Nebulae
The prevalence and energetics of quasar feedback is a major unresolved
problem in galaxy formation theory. In this paper, we present Gemini Integral
Field Unit observations of ionized gas around eleven luminous, obscured,
radio-quiet quasars at z~0.5 out to ~15 kpc from the quasar; specifically, we
measure the kinematics and morphology of [O III]5007 emission. The round
morphologies of the nebulae and the large line-of-sight velocity widths (with
velocities containing 80% of the emission as high as 1000 km/s combined with
relatively small velocity difference across them (from 90 to 520 km/s) point
toward wide-angle quasi-spherical outflows. We use the observed velocity widths
to estimate a median outflow velocity of 760 km/s, similar to or above the
escape velocities from the host galaxies. The line-of-sight velocity dispersion
declines slightly toward outer parts of the nebulae (by 3% per kpc on average).
The majority of nebulae show blueshifted excesses in their line profiles across
most of their extents, signifying gas outflows. For the median outflow
velocity, we find a kinetic energy flow between 4x10^{44} and 3x10^{45} erg/s
and mass outflow rate between 2000 and 20000 Msun/yr. These values are large
enough for the observed quasar winds to have a significant impact on their host
galaxies. The median rate of converting bolometric luminosity to kinetic energy
of ionized gas clouds is ~2%. We report four new candidates for "super-bubbles"
-- outflows that may have broken out of the denser regions of the host galaxy.Comment: 23 pages, 10 figures, 2 tables, accepted for publication in MNRA
Probing the Mpc-scale environment of hyperluminous infrared galaxies at 2<z<4
Protoclusters are important for studying how halo mass and stellar mass
assemble in the early universe. Finding signposts of such over-dense regions is
a popular method to identify protocluster candidates. Hyperluminous infrared
galaxies (HLIRGs), are expected to reside in overdense regions with massive
halos. We study the Mpc-scale environment of the largest HLIRG sample to date
and investigate whether they predominantly live in overdense regions. We first
explore the surface density of Herschel 250 m sources around HLIRGs and
compare with that around random positions. Then, we compare the spatial
distribution of neighbours around HLIRGs with that around randomly selected
galaxies using a deep IRAC-selected catalogue with good-quality photometric
redshifts. We also use a redshift-matched quasar sample and submillimeter
galaxy (SMG) sample to validate our method, as previous clustering studies have
measured the host halo masses of these populations. Finally, we adopt a Friends
of Friends (FOF) algorithm to seek (proto)clusters that host HLIRGs. We find
that HLIRGs tend to have more bright star-forming neighbours (with 250 m
flux density >10 mJy) within 100\arcsec projected radius than a random galaxy
at a 3.7 significance. In our 3D analysis, we find relatively weak
excess of IRAC-selected sources within 3 Mpc around HLIRGs compared with random
galaxy neighbours, mainly influenced by photometric redshift uncertainty and
survey depth. We find a more significant difference (at a 4.7
significance) in the number of Low Frequency Array (LOFAR)-detected neighbours
in the deepest EN1 field. HLIRGs at 3 < z < 4 show stronger excess compared to
HLIRGs at 2 < z < 3, consistent with cosmic downsizing. Finally, we select and
present a list of 30 most promising protocluster candidates for future
follow-up observations.Comment: 19 pages, 10 figures, accepted by A&
Binary black holes and tori in AGN II. Can stellar winds constitute a dusty torus?
We determine the properties of the stellar torus that we showed in a previous
paper to result as a product of two merging black holes. If the surrounding
stellar cluster is as massive as the binary black hole, the torque acting on
the stars ejects a fraction which extracts all the binary's angular momentum on
scales of ~10^7 yr, and a geometrically thick torus remains. In the present
article we show that a certain fraction of the stars has winds, shaped into
elongated tails by the central radiation pressure, which are optically thick
for line of sights aligned with them. These stars are sufficiently numerous to
achieve a covering factor of 1, so that the complete torus is optically thick.
We find the parameters of such a patchy torus to be in the right range to
explain the observed large column densities in AGN and their temporal
variations on time scales of about a decade. Within this model the BAL quasars
can be interpreted as quasars seen at intermediate inclination angles, with the
line of sight grazing the edge of the torus. The opening angle of the torus is
wider for major mergers and thus correlates with the central luminosity. In
this picture the spin of the merged black hole is possibly dominated by the
orbital angular momentum of the binary. Thus the spin of the merged black hole
points into a new direction, and consequently the jet experiences a spin-flip
according to the spin-paradigm. This re-orientation could be an explanation for
the X-shaped radio galaxies, and the advancing of a new jet through the ambient
medium for Compact Symmetric Objects.Comment: 20 pages, 10 figures, final version, A&A accepte
Coevolution of supermassive Black Holes and Galaxies across cosmic times
Understanding how supermassive black holes (SMBHs) and galaxies coevolve within their host dark matter (DM) halos is a fundamental issue in astrophysics. This thesis is aimed to shed light on this topic. As a rst step, we employ the recent wide samples of far-infrared (FIR) selected galaxies followed-up in X-rays, and of X-ray/optically selected active galactic nuclei (AGNs) followed-up in the FIR band, along with the classic data on AGN and stellar luminosity functions at redshift z & 1:5, to probe different stages in the coevolution of SMBHs and their host galaxies. The results of this analysis indicate the following scenario: (i) the star formation in the host galaxy proceeds within a heavily dust-enshrouded medium, at an almost constant rate, over a timescale . 0:5 1 Gyr, and then abruptly declines due to quasar feedback; (ii) part of the interstellar medium loses angular momentum, reaches the circum-nuclear regions, at a rate proportional to the star formation, and is temporarily stored into a massive reservoir/proto-torus, wherefrom it can be promptly accreted; (iii) the black hole (BH) grows by accretion in a self-regulated regime with radiative power that can slightly exceed the Eddington limit (L=LEdd . 4), particularly at the highest redshifts; (iv) the ensuing energy feedback from massive BHs, at its maximum, exceeds the stellar one and removes the interstellar gas, thus stopping the star formation and the fueling of the reservoir; (v) afterwards, if the gas stored in the reservoir is enough, a phase of supply-limited accretion follows, whose rate exponentially declines with a timescale of 3 e-folding times. We also discuss how the detailed properties and the speci c evolution of the reservoir can be investigated via coordinated, high-resolution observations of starforming, strongly lensed galaxies in the (sub-)mm band with ALMA, and in the X-ray band with Chandra and the next generation of X-ray instruments. According to the scenario described above, we further investigate the coevolution of galaxies and hosted SMBHs throughout the history of the Universe by applying a statis- tical, model-independent approach, based on the continuity equation and the abundance matching technique. We present analytical solutions of the continuity equation with- out source term, to reconstruct the SMBH mass function (BHMF) at different redshifts from the AGN luminosity function. Such an approach includes the physically-motivated AGN lightcurves we have tested and discussed, which describe the evolution of both the Eddington ratio and the radiative efficiency from slim- to thin-disc conditions. We nicely reproduce the local estimates of the BHMF, the AGN duty cycle as a function of mass and redshift, along with the Eddington ratio function and the fraction of galaxies hosting an AGN with given Eddington ratio. We employ the same approach to reconstruct the observed stellar mass function (SMF) at different redshifts, starting from the ultraviolet (UV) and FIR luminosity functions associated to star formation in galaxies. Our results imply that the buildup of stars and BHs in galaxies occurs via in-situ processes, with dry mergers playing a marginal role, at least for stellar masses . 3 1011M 99 and BH masses . 109M 99, where the statistical data are more secure and less biased by systematic errors. In addition, we develop an improved abundance matching technique, to link the stellar and BH content of galaxies to the gravitationally dominant DM component. The re- sulting relationships constitute a testbed for galaxy evolution models, highlighting the complementary role of stellar and AGN feedback in the star formation process. They may also be operationally implemented in numerical simulations to populate DM ha- los, or to gauge subgrid physics. Moreover, they can be exploited to investigate the galaxy/AGN clustering as a function of redshift, stellar/BH mass, and/or luminosity. The clustering properties of BHs and galaxies are found to be in full agreement with current observations, so further validating our results from the continuity equation. Finally, our analysis highlights that: (i) the fraction of AGNs observed in the slim-disc regime, where anyway most of the BH mass is accreted, increases with redshift; (ii) already at z & 6, a substantial amount of dust must have formed, over timescales . 108 yr, in strongly starforming galaxies, making these sources well within the reach of ALMA surveys in (sub-)millimeter bands
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