Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userGemini imaging of QSO host galaxies at z~2
68
0
0.0
(
0
)
Authors
Scott Croom
Ask ChatGPT about the research
No Arabic abstract
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.
rate research
Read More
We report on deep imaging in 2 filters with the PC2 camera of HST, of five QSOs at redshift ~2, with a range of optical and radio luminosity. The observations included a suite of PSF observations which were used to construct new PSF models, described elsewhere by Dumont et al. The new PSF models were used to remove the QSO nucleus from the images. We find that the host galaxies have resolved flux of order 10% of the QSO nuclei, and are generally luminous and blue, indicating active star-formation. While most have clearly irregular morphologies, the bulk of the flux can be modelled approximately by an r**1/4 law. However, all host galaxies also have an additional approximately exponential luminosity profile beyond a radius about 0.8 arcsec, as also seen in ground-based data with larger telescopes. The QSOs all have a number of nearby faint blue companions which may be young galaxies at the QSO redshift. We discuss implications for evolution of the host galaxies, their spheroidal populations, and central black holes.
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.
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 report near-infrared (primarily H-band) adaptive optics (AO) imaging with the Gemini-N and Subaru Telescopes, of a representative sample of 32 nearby (z<0.3) QSOs selected from the Palomar-Green (PG) Bright Quasar Survey (BQS), in order to investigate the properties of the host galaxies. 2D modeling and visual inspection of the images shows that ~36% of the hosts are ellipticals, ~39% contain a prominent disk component, and ~25% are of undetermined type. 30% show obvious signs of disturbance. The mean M_H(host) = -24.82 (2.1L_H*), with a range -23.5 to -26.5 (~0.63 to 10 L_H*). At <L_H*, all hosts have a dominant disk component, while at >2 L_H* most are ellipticals. Disturbed hosts are found at all M_H(host), while strongly disturbed hosts appear to favor the more luminous hosts. Hosts with prominent disks have less luminous QSOs, while the most luminous QSOs are almost exclusively in ellipticals or in mergers (which presumably shortly will be ellipticals). At z<0.13, where our sample is complete at B-band, we find no clear correlation between M_B(QSO) and M_H(host). However, at z>0.15, the more luminous QSOs (M_B<-24.7), and 4/5 of the radio-loud QSOs, have the most luminous H-band hosts (>7L_H*), most of which are ellipticals. Finally, we find a strong correlation between the infrared-excess, L_IR/L_BB, of QSOs with host type and degree of disturbance. Disturbed and strongly disturbed hosts and hosts with dominant disks have L_IR/L_BB twice that of non-disturbed and elliptical hosts, respectively. QSOs with disturbed and strongly-disturbed hosts are also found to have morphologies and mid/far-infrared colors that are similar to what is found for warm ultraluminous infrared galaxies, providing further evidence for a possible evolutionary connection between both classes of objects.
Changing-look quasars are a newly-discovered class of luminous active galactic nuclei that undergo rapid ($lesssim$10 year) transitions between Type 1 and Type 1.9/2, with an associated change in their continuum emission. We characterize the host galaxies of four faded changing-look quasars using broadband optical imaging. We use textit{gri} images obtained with the Gemini Multi Object Spectrograph (GMOS) on Gemini North to characterize the surface brightness profiles of the quasar hosts and search for [O III] $lambda4959,lambda5007$ emission from spatially extended regions, or voorwerpjes, with the goal of using them to examine past luminosity history. Although we do not detect, voorwerpjes surrounding the four quasar host galaxies, we take advantage of the dim nuclear emission to characterize the colors and morphologies of the host galaxies. Three of the four galaxies show morphological evidence of merger activity or tidal features in their residuals. The three galaxies which are not highly distorted are fit with a single Sersic profile to characterize their overall surface brightness profiles. The single-Sersic fits give intermediate Sersic indices between the $n=1$ of disk galaxies and the $n=4$ of ellipticals. On a color-magnitude diagram, our changing-look quasar host galaxies reside in the blue cloud, with other AGN host galaxies and star-forming galaxies. On a color-Sersic index diagram the changing-look quasar hosts reside with other AGN hosts in the green valley. Our analysis suggests that the hosts of changing-look quasars are predominantly disrupted or merging galaxies that resemble AGN hosts, rather than inactive galaxies.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
