Warm and Cold Molecular Gas in Luminous Infrared Galaxies

We present the properties of the warm and cold molecular gas in a sample of local Luminous Infrared Galaxies in the Great Observatories All-sky LIRG Survey (GOALS). The rotational transitions of H_2 observed in the Mid-Infrared Spectra from the Spitzer Survey trace gas at temperatures about 100K, while the 12 CO (1-0) maps acquired with the Combined Array for Millimeter Astronomy identify the morphology of the cold (less than 40K). The 17.1 μm S(1) transitions of warm H_2 is detected in 94% of the 247 LIRG nuclei analyzed. The warm H_2 S(0) to S(3) emission is correlated with the 6.2 μm and the [Si II] cooling line. This suggests that the H_2 is mostly excited in PDR. The large scatter in correlation both for merging and non-merging sources suggests that some of the excitation appear to be due to shocks associated with SNe. This is consistent with the high fractions of [FeII]/[OIV] ≥ 1 we measure in about 20% of the sources and the number of sources with detected S(7) emission. The larger scatter in the PAH to H_2 may also be due to both the presence of an AGN hard ionizing continuum and the the large range of interactions observed in LIRGs (about 50% of LIRGs in GOALs are interacting). The 16 12CO(1-0) maps for LIRGs in a merger sequence show that molecular gas surface densities range between about 65 M_☉/pc^2 to 2600 M_☉/pc^2 with a median and mean value of 290 and 571 M^☉/pc^2 respectively. This suggests that LIRGs have a wide range of molecular gas surfaces but in general a factor of a few greater than normal galaxies and not the extreme values seen typically in Ultraluminous Infrared Galaxies (ULIRGs) or PG QSOs. We find that molecular gas depletion times increase with merger stage but do not appear to vary with stellar mass

Herschel Survey of the Palomar-Green QSOs at Low Redshift

We investigate the global cold dust properties of 85 nearby (z < 0.5) QSOs, chosen from the Palomar-Green sample of optically luminous quasars. We determine their infrared spectral energy distributions and estimate their rest-frame luminosities by combining Herschel data from 70 to 500 microns with near-infrared and mid-infrared measurements from the Two Micron All Sky Survey (2MASS) and the Wide-Field Infrared Survey Explorer (WISE). In most sources the far-infrared (FIR) emission can be attributed to thermally heated dust. Single temperature modified black body fits to the FIR photometry give an average dust temperature for the sample of 33~K, with a standard deviation of 8~K, and an average dust mass of 7E6 Solar Masses with a standard deviation of 9E6 Solar Masses. Estimates of star-formation that are based on the FIR continuum emission correlate with those based on the 11.3 microns PAH feature, however, the star-formation rates estimated from the FIR continuum are higher than those estimated from the 11.3 microns PAH emission. We attribute this result to a variety of factors including the possible destruction of the PAHs and that, in some sources, a fraction of the FIR originates from dust heated by the active galactic nucleus and by old stars.Comment: accepted for publication in ApJ

Quantifying Roman WFI Dark Images with the Wavelet Scattering Transform

The Nancy Grace Roman Space Telescope will survey a large area of the sky at near-infrared wavelengths with its Wide Field Instrument (WFI). The performance of the 18 WFI H4RG-10 detectors will need to be well-characterized and regularly monitored in order for Roman to meet its science objectives. Weak lensing science goals are particularly sensitive to instrumental distortions and patterns that might masquerade as astronomical signals. We apply the wavelet scattering transform in order to analyze localized signals in Roman WFI images that have been taken as part of a dark image test suite. The scattering transform quantifies shapes and clustering information by reducing images into non-linear combinations of wavelet modes on multiple size scales. We show that these interpretable scattering statistics can separate rare correlated patterns from typical noise signals, and we discuss the results in context of power spectrum analyses and other computer vision methods.Comment: 14 pages, 4 figures, accepted to PAS

A Direct Upper Limit on the Density of Cosmological Dust from the Absence of an X-ray Scattering Halo around the z=4.3 QSO 1508+5714

We report on the results of a search for an intergalactic X-ray dust scattering halo in a deep observation of the bright, high-redshift quasar QSO 1508+5714 with the Chandra X-ray Observatory. We do not detect such a halo. Our result implies an upper limit on the density of diffuse, large-grained intergalactic dust of Omega_ dust < 2 x 10^-6, assuming a characteristic grain size of 1micron. The result demonstrates the sensitivity of this technique for detecting very small amounts of intergalactic dust which are very hard to detect otherwise. This will allow us to put important constraints on systematic effects induced by extinction on the interpretation of the SN Ia Hubble Diagram, as well as on the amount and properties of cosmological dust being expelled into the intergalactic medium at early z~2 times.Comment: 14 pages, 2 figures. to appear in ApJ, vol. 651, Nov. 200

The stellar, molecular gas and dust content of the host galaxies of two z~2.8 dust obscured quasars

We present optical through radio observations of the host galaxies of two dust obscured, luminous quasars selected in the mid-infrared, at z=2.62 and z=2.99, including a search for CO emission. Our limits on the CO luminosities are consistent with these objects having masses of molecular gas <~10^10 solar masses, several times less than those of luminous submillimeter-detected galaxies (SMGs) at comparable redshifts. Their near-infrared spectral energy distributions, however, imply that these galaxies have high stellar masses (~10^11-12 solar masses). The relatively small reservoirs of molecular gas and low dust masses are consistent with them being relatively mature systems at high-z.Comment: AJ, in pres

The Spitzer mid-infrared AGN survey. II-the demographics and cosmic evolution of the AGN population

We present luminosity functions derived from a spectroscopic survey of AGN selected from Spitzer Space Telescope imaging surveys. Selection in the mid-infrared is significantly less affected by dust obscuration. We can thus compare the luminosity functions of the obscured and unobscured AGN in a more reliable fashion than by using optical or X-ray data alone. We find that the AGN luminosity function can be well described by a broken power-law model in which the break luminosity decreases with redshift. At high redshifts ($z>1.6$), we find significantly more AGN at a given bolometric luminosity than found by either optical quasar surveys or hard X-ray surveys. The fraction of obscured AGN decreases rapidly with increasing AGN luminosity, but, at least at high redshifts, appears to remain at $\approx 50$\% even at bolometric luminosities $\sim 10^{14}L_{\odot}$. The data support a picture in which the obscured and unobscured populations evolve differently, with some evidence that high luminosity obscured quasars peak in space density at a higher redshift than their unobscured counterparts. The amount of accretion energy in the Universe estimated from this work suggests that AGN contribute about 12\% to the total radiation intensity of the Universe, and a high radiative accretion efficiency $\approx 0.18^{+0.12}_{-0.07}$ is required to match current estimates of the local mass density in black holes.Comment: 14 pages, accepted by Ap

Spitzer Observations of Young Red Quasars

We present mid-infrared spectra and photometry of 13 redshift 0.4 < z < 1 dust reddened quasars obtained with Spitzer IRS and MIPS. We compare properties derived from their infrared spectral energy distributions (intrinsic active galactic nucleus (AGN) luminosity and far-infrared luminosity from star formation) to the host luminosities and morphologies from Hubble Space Telescope imaging, and black hole masses estimated from optical and/or near-infrared spectroscopy. Our results are broadly consistent with models in which most dust reddened quasars are an intermediate phase between a merger-driven starburst triggering a completely obscured AGN, and a normal, unreddened quasar. We find that many of our objects have high accretion rates, close to the Eddington limit. These objects tend to fall below the black hole mass-bulge luminosity relation as defined by local galaxies, whereas most of our low accretion rate objects are slightly above the local relation, as typical for normal quasars at these redshifts. Our observations are therefore most readily interpreted in a scenario in which galaxy stellar mass growth occurs first by about a factor of three in each merger/starburst event, followed sometime later by black hole growth by a similar amount. We do not, however, see any direct evidence for quasar feedback affecting star formation in our objects, for example, in the form of a relationship between accretion rate and star formation. Five of our objects, however, do show evidence for outflows in the [O III]5007 Å emission line profile, suggesting that the quasar activity is driving thermal winds in at least some members of our sample