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Register a new userMolecular gas in QSO host galaxies at z>5
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We present observations with the IRAM Plateau de Bure Interferometer of three QSOs at z>5 aimed at detecting molecular gas in their host galaxies as traced by CO transitions. CO (5-4) is detected in SDSSJ033829.31+002156.3 at z=5.0267, placing it amongst the most distant sources detected in CO. The CO emission is unresolved with a beam size of ~1, implying that the molecular gas is contained within a compact region, less than ~3kpc in radius. We infer an upper limit on the dynamical mass of the CO emitting region of ~3x10^10 Msun/sin(i)^2. The comparison with the Black Hole mass inferred from near-IR data suggests that the BH-to-bulge mass ratio in this galaxy is significantly higher than in local galaxies. From the CO luminosity we infer a mass reservoir of molecular gas as high as M(H2)=2.4x10^10 Msun, implying that the molecular gas accounts for a significant fraction of the dynamical mass. When compared to the star formation rate derived from the far-IR luminosity, we infer a very short gas exhaustion timescale (~10^7 yrs), comparable to the dynamical timescale. CO is not detected in the other two QSOs (SDSSJ083643.85+005453.3 and SDSSJ163033.90+401209.6) and upper limits are given for their molecular gas content. When combined with CO observations of other type 1 AGNs, spanning a wide redshift range (0<z<6.4), we find that the host galaxy CO luminosity (hence molecular gas content) and the AGN optical luminosity (hence BH accretion rate) are correlated, but the relation is not linear: L(CO) ~ [lambda*L_lambda(4400A)]^0.72. Moreover, at high redshifts (and especially at z>5) the CO luminosity appears to saturate. We discuss the implications of these findings in terms of black hole-galaxy co-evolution.
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We present results of a Gemini adaptive optics (AO) imaging program to investigate the host galaxies of typical QSOs at z~2. Our aim is to study the host galaxies of typical, L*_qso QSOs at the epoch of peak QSO and star formation activity. The large database of faint QSOs provided by the 2dF QSO Redshift Survey allows us to select a sample of QSOs at z=1.75-2.5 which have nearby (<12 arcsecond separation) bright stars suitable for use as AO guide stars. We have observed a sample of 9 QSOs. The images of these sources have AO corrected full-width at half-maximum of between 0.11 and 0.25 arcseconds. We use multiple observations of point spread function (PSF) calibration star pairs in order to quantify any uncertainty in the PSF. We then factored these uncertainties into our modelling of the QSO plus host galaxy. In only one case did we convincingly detect a host (2QZ J133311.4+001949, at z=1.93). This host galaxy has K=18.5+-0.2 mag with a half-light radius, r_e=0.55+-0.1, equivalent to ~3L*_gal assuming a simple passively evolving model. From detailed simulations of our host galaxy modelling process, we find that for four of our targets we should be sensitive to host galaxies that are equivalent to ~2L*_gal (passively evolved). Our non-detections therefore place tight constraints on the properties of L*_qso QSO host galaxies, which can be no brighter (after allowing for passive evolution) than the host galaxies of L*_qso AGN at low redshift, although the QSOs themselves are a factor of ~50 brighter. This implies that either the fueling efficiency is much greater at high redshift, or that more massive black holes are active at high redshift.
Aims. We aim to search and characterize inflows and outflows of molecular gas in four ultraluminous infrared galaxies (ULIRGs) at $zsim0.2-0.3$ and one distant QSO at $z=6.13$. Methods. We use Herschel PACS and ALMA Band 7 observations of the hydroxyl molecule (OH) line at rest-frame wavelength 119 $mu$m which in absorption can provide unambiguous evidence for inflows or outflows of molecular gas in nuclear regions of galaxies. Our study contributes to double the number of OH observations of luminous systems at $zsim0.2-0.3$, and push the search for molecular outflows based on the OH transition to $zsim6$. Results. We detect OH high-velocity absorption wings in three of the four ULIRGs. In two cases, IRAS F20036-1547 and IRAS F13352+6402, the blueshifted absorption profiles indicate the presence of powerful and fast molecular gas outflows. Consistent with an inside-out quenching scenario, these outflows are depleting the central reservoir of molecular gas at a similar rate than the intense star formation activity. In the case of the starburst-dominated system IRAS 10091+4704, we detect an inverted P-Cygni profile that is unique among ULIRGs and indicates the presence of a fast ($sim400$ km s$^{-1}$) inflow of molecular gas at a rate of $sim100~M_{odot}~{rm yr}^{-1}$ towards the central region. Finally, we tentatively detect ($sim3sigma$) the OH doublet in absorption in the $z=6.13$ QSO ULAS J131911+095051. The OH feature is blueshifted with a median velocity that suggests the presence of a molecular outflow, although characterized by a modest molecular mass loss rate of $sim200~M_{odot}~{rm yr}^{-1}$. This value is comparable to the small mass outflow rates found in the stacking of the [CII] spectra of other $zsim6$ QSOs and suggests that ejective feedback in this phase of the evolution of ULAS J131911+095051 has subsided.
We present new imaging and spectroscopic observations of the fields of five QSOs with very strong intervening CaII absorption systems at redshifts z<0.5 selected from the Sloan Digital Sky Survey. Recent studies of these very rare absorbers indicate that they may be related to damped Lyman alpha systems (DLAs). In all five cases we identify a galaxy at the redshift of the CaII system with impact parameters up to ~24 kpc. In four out of five cases the galaxies are luminous (L ~L*), metal-rich (Z ~Zsun), massive (velocity dispersion, sigma ~100 km/s) spirals. Their star formation rates, deduced from Halpha emission, are high, in the range SFR = 0.3 - 30 Msun/yr. In our analysis, we paid particular attention to correcting the observed emission line fluxes for stellar absorption and dust extinction. We show that these effects are important for a correct SFR estimate; their neglect in previous low-z studies of DLA-selected galaxies has probably led to an underestimate of the star formation activity in at least some DLA hosts. We discuss possible links between CaII-selected galaxies and DLAs and outline future observations which will help clarify the relationship between these different classes of QSO absorbers.
We present high-resolution VLA observations of the molecular gas in the host galaxy of the highest redshift quasar currently known, SDSS J1148+5251 (z=6.42). Our VLA data of the CO(3-2) emission have a maximum resolution of 0.17 x 0.13 (~1 kpc), and enable us to resolve the molecular gas emission both spatially and in velocity. The molecular gas in J1148+5251 is extended to a radius of 2.5 kpc, and the central region shows 2 peaks, separated by 0.3 (1.7 kpc). These peaks account for about half of the total emission, while the remainder is more extended. Each of these unresolved peaks contains a molecular gas mass of ~5 x 10^9 M_sun (similar to the total mass found in nearby ULIRGS) and has an intrinsic brightness temperature of ~35 K (averaged over the 1 kpc-sized beam), comparable to what is found in nearby starburst centers. Assuming that the molecular gas is gravitationally bound, we estimate a dynamical mass of ~4.5 x 10^10 M_sun within a radius of 2.5 kpc (~5.5 x 10^10 M_sun if corrected for a derived inclination of i~65 deg.). This dynamical mass estimate leaves little room for matter other than the detected molecular gas, and in particular the data are inconsistent with a ~10^12 M_sun stellar bulge which would be predicted based on the M_BH-sigma_bulge relation. This finding may indicate that black holes form prior to the assembly of the stellar bulges and that the dark matter halos are less massive than predicted based on the black hole/bulge mass relationship.
Many of the conditions that are necessary for starbursts appear to be important in the triggering of QSOs. However, it is still debatable whether starbursts are ubiquitously present in galaxies harboring QSOs. In this paper we review our current knowledge from observations of the role of starbursts in different types of QSOs. Post-starburst stellar populations are potentially present in the majority of QSO hosts. QSOs with far-infrared colors similar to those of ultraluminous infrared galaxies invariably reside in merging galaxies that have interaction-induced starbursts of a few hundred Myr or less. Similar, but dramatically more luminous post-starburst populations are found in the recently discovered class of QSOs known as post-starburst QSOs, or Q+As. Both of these classes, however, comprise only a small fraction (10-15%) of the total QSO population. The so-called red QSOs generally suffer from strong extinction at optical wavelengths, making them ideal candidates for the study of hosts. Their stellar populations typically show a post-starburst component as well, though with a larger range of ages. Finally, optical classical QSO hosts show traces of major star formation episodes (typically involving >10% of the mass of the stellar component) in the more distant past (1-2 Gyr). These starbursts appear to be linked to past merger events. It remains to be determined whether these mergers were also responsible for triggering the QSO activity that we observe today.
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