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Register a new userA 1.2mm MAMBO/IRAM-30m Study of Dust Emission from optically luminous z~2 Quasars
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A. Omont
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We report 250GHz (1.2mm) observations of redshift 1.8 < z < 2.8 optically luminous (M_B < -27.0), radio quiet quasars using the Max-Planck Millimeter Bolometer (MAMBO) array at the IRAM 30-metre telescope. Nine quasars were detected and for 26 quasars 3-sigma flux density limits in the range 1.8 to 4mJy were obtained. Adopting a typical dust temperature of 45K, the millimeter emission implies far-infrared (FIR) luminosities of order 10^13 Lo and dust masses of ~10^8 Mo. Applying a statistical survival analysis to our total sample of 43 detected and 95 undetected quasars at z~2 and z>4, we find that there is no apparent difference in the FIR luminosities, hence the star formation rates, of QSO at z~2 and at 3.6< z <5. This differs from radio galaxies, for which the FIR luminosity was found to increase with redshift (Archibald et al. 2001). We furthermore find that there is no strong correlation between the far-infrared and optical luminosities, confirming previous results obtained on smaller samples.
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We report on--off pointed MAMBO observations at 1.2 mm of 61 Spitzer-selected star-forming galaxies from the SWIRE survey. The sources are selected on the basis of bright 24um fluxes (f_24um>0.4mJy) and of stellar dominated near-infrared spectral energy distributions in order to favor z~2 starburst galaxies. The average 1.2mm flux for the whole sample is 1.5+/-0.2 mJy. Our analysis focuses on 29 sources in the Lockman Hole field where the average 1.2mm flux (1.9+/-0.3 mJy) is higher than in other fields (1.1+/-0.2 mJy). The analysis of the sources multi-wavelength spectral energy distributions indicates that they are starburst galaxies with far-infrared luminosities ~10^12-10^13.3 Lsun, and stellar masses of ~0.2-6 x10^11 M_sun. Compared to sub-millimeter selected galaxies (SMGs), the SWIRE-MAMBO sources are among those with the largest 24um/millimeter flux ratios. The origin of such large ratios is investigated by comparing the average mid-infrared spectra and the stacked far-infrared spectral energy distributions of the SWIRE-MAMBO sources and of SMGs. The mid-infrared spectra exhibit strong PAH features, and a warm dust continuum. The warm dust continuum contributes to ~34% of the mid-infrared emission, and is likely associated with an AGN component. This constribution is consistent with what is found in SMGs. The large 24um/1.2mm flux ratios are thus not due to AGN emission, but rather to enhanced PAH emission compared to SMGs. The analysis of the stacked far-infrared fluxes yields warmer dust temperatures than typically observed in SMGs. Our selection favors warm ultra-luminous infrared sources at high-z, a class of objects that is rarely found in SMG samples. Our sample is the largest Spitzer-selected sample detected at millimeter wavelengths currently available.
We present a search for CO emission in a sample of ten type-2 quasar host galaxies with redshifts of z=0.1-0.4. We detect CO(J=1-0) line emission with >=5sigma in the velocity integrated intensity maps of five sources. A sixth source shows a tentative detection at the ~4.5sigma level of its CO(J=1-0) line emission. The CO emission of all six sources is spatially coincident with the position at optical, infrared or radio wavelengths. The spectroscopic redshifts derived from the CO(J=1-0) line are very close to the photometric ones for all five detections except for the tentative detection for which we find a much larger discrepancy. We derive gas masses of ~(2-16)x10^9Msun for the CO emission in the six detected sources, while we constrain the gas masses to upper limits of Mgas<=8x10^9Msun for the four non-detections. These values are of the order or slightly lower than those derived for type-1 quasars. The line profiles of the CO(J=1-0) emission are rather narrow (<=300km/s) and single peaked, unveiling no typical signatures for current or recent merger activity, and are comparable to that of type-1 quasars. However, at least one of the observed sources shows a tidal-tail like emission in the optical that is indicative for an on-going or past merging event. We also address the problem of detecting spurious ~5sigma emission peaks within the field of view.
We have obtained H-band spectra of 32 luminous quasars at 2.0<z<2.5 with the Multiple Mirror Telescope. The sample contains 15 radio-loud quasars (RLQs) and 17 radio-quiet quasars (RQQs). We have measured emission line properties from the rest-frame wavelength range of approximately 4500-5500 Angstroms, by fitting the data with composite model spectra. Our analysis includes comparison of RLQs versus RQQs, as well as comparison between the broad-absorption-line quasar (BALQSO) and non-broad-absorption-line quasar (nonBALQSO) subsets of the RQQ sample. In addition, we calculated the complete correlation matrix of the measured properties. We combined our high redshift sample with the sample of 87 low redshift quasars from Boroson & Green (1992) to determine the luminosity and redshift dependences of the measured emission properties. Our main results are: (1) The RLQ sample has significantly stronger [O III]5007 emission than the RQQ sample. (2) The RLQ sample has significantly narrower (in FWHM) Hbeta broad component line profiles than the RQQ sample. (3) At the sensitivity of our observations, there are no statistically significant (>95%) differences between the rest-frame optical emission line properties of the BALQSO and nonBALQSO subsamples. This result is consistent with the view that all RQQs have broad-absorption-line clouds with a small (~10-20%) covering factor and that differences between the two types are merely a function of viewing angle and covering factor. (4) We report a previously unknown luminosity and/or redshift dependence of the narrow-line-region velocity width over the range 0<z<2.5, such that emission line widths increase with increasing luminosity. Furthermore, we find a ``Baldwin Effect for the [O III]5007 line in the RQQ-only sample over this same range in redshifts.
We present H-band observations of gravitationally lensed QSO host galaxies obtained with NICMOS on HST as part of the CfA-Arizona-Gravitational-Lens-Survey (CASTLES). The detections are greatly facilitated by the lensing magnification in these systems; we find that most hosts of radio-quiet QSOs (RQQ) at z~2 are of modest luminosity (L<L_*). They are 2-5 times fainter than the hosts of radio-loud QSOs at the same epoch. Compared to low redshifts, RQQ hosts at z~2 also support higher nuclear luminosities at given stellar host mass. This suggests that the supermassive black holes at their centers grew faster at early epochs than the stellar body of their surrounding host galaxies.
With close pairs of quasars at different redshifts, a background quasar sightline can be used to study a foreground quasars environment in absorption. We search 149 moderate resolution background quasar spectra, from Gemini, Keck, the MMT, and the SDSS to survey Lyman Limit Systems (LLSs) and Damped Ly-alpha systems (DLAs) in the vicinity of 1.8 < z < 4.0 luminous foreground quasars. A sample of 27 new quasar-absorber pairs is uncovered with column densities, 17.2 < log (N_HI/cm^2) < 20.9, and transverse (proper) distances of 22 kpc/h < R < 1.7 Mpc/h, from the foreground quasars. If they emit isotropically, the implied ionizing photon fluxes are a factor of ~ 5-8000 times larger than the ambient extragalactic UV background over this range of distances. The observed probability of intercepting an absorber is very high for small separations: six out of eight projected sightlines with transverse separations R < 150 kpc/h have an absorber coincident with the foreground quasar, of which four have log N_HI > 10^19. The covering factor of log N_HI > 10^19 absorbers is thus ~ 50 % (4/8) on these small scales, whereas < 2% would have been expected at random. There are many cosmological applications of these new sightlines: they provide laboratories for studying fluorescent Ly-alpha recombination radiation from LLSs, constrain the environments, emission geometry, and radiative histories of quasars, and shed light on the physical nature of LLSs and DLAs.
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