Black hole feedback is now a standard component of galaxy formation models. These models predict that the impact of black hole activity on its host galaxy likely peaked at z = 2–3, the epoch of ...strongest star formation activity and black hole accretion activity in the Universe. We used XShooter on the Very Large Telescope to measure rest-frame optical spectra of four z ∼ 2.5 extremely red quasars with infrared luminosities ∼1047 erg s−1. We present the discovery of very broad (full width at half max = 2600–5000 km s−1), strongly blueshifted (by up to 1500 km s−1) O iii λ5007 Å emission lines in these objects. In a large sample of type 2 and red quasars, O iii kinematics are positively correlated with infrared luminosity, and the four objects in our sample are on the extreme end in both O iii kinematics and infrared luminosity. We estimate that at least 3 per cent of the bolometric luminosity in these objects is being converted into the kinetic power of the observed wind. Photo-ionization estimates suggest that the O iii emission might be extended on a few kpc scales, which would suggest that the extreme outflow is affecting the entire host galaxy of the quasar. These sources may be the signposts of the most extreme form of quasar feedback at the peak epoch of galaxy formation, and may represent an active ‘blow-out’ phase of quasar evolution.
ABSTRACT Major gas-rich mergers of galaxies are expected to play an important role in triggering and fueling luminous active galactic nuclei (AGNs). The mechanism of AGN fueling during mergers, ...however, remains poorly understood. We present deep multi-band ( ) imaging and long-slit spectroscopy of four double-peaked emitting AGNs. This class of object is likely associated with either kiloparsec-separated binary AGNs or final stage major mergers, although AGNs with complex narrow-line regions (NLRs) are known contaminants. Such objects are of interest since they represent the onset of AGN activity during the merger process. Three of the four double-peaked emitters studied have been confirmed as major mergers using near-infrared imaging and one is a confirmed X-ray binary AGN. All AGNs are luminous, radio-quiet to radio-intermediate, and have redshifts of . Deep r-band images show that a majority (3/4) of the sources have disturbed host morphologies and tidal features, while the remaining source is morphologically undisturbed down to low surface brightness limits (∼27 mag arcsec−2 in r). The lack of morphological disturbances in this galaxy despite the fact that it is a close binary AGN suggests that the merger of a binary black hole can take longer than 1 Gyr. All AGNs hosted by merging galaxies have companions at distances 150 kpc. The NLRs have large sizes (10 kpc 100 kpc) and consist of compact clumps with considerable relative velocities between components (∼200-650 km s−1). We detect broad, predominantly blue, wings with velocities up to ∼1500 km s−1 in , indicative of powerful outflows. The outflows are compact ( kpc) and co-spatial with nuclear regions showing considerable reddening, consistent with enhanced star formation. One source shows an offset between gas and stellar kinematics, consistent with either a bipolar flow or a counter-rotating gas disk. In all other sources, the ionized gas generally follows the stars. We are not able to unambiguously identify the sources as binary AGNs using our data; X-ray or radio data are required for an unambiguous identification. However, the data still yield interesting results for merger triggering of AGNs and timescales of binary black hole mergers.
Intranight polarization variability in active galactic nuclei (AGN) has not been studied extensively so far. Studying the variability in polarization makes it possible to distinguish between ...different emission mechanisms. Thus, it can help answering the question if intranight variability in radio-loud and radio-quiet AGN is of the same or of fundamentally different origin. In this paper, we investigate intranight polarization variability in AGN. Our sample consists of 28 AGN at low to moderate redshifts (0.048 ≤z≤ 1.036), 12 of which are radio-quiet quasars (RQQs) and 16 are radio-loud blazars. The subsample of blazars consists of eight flat-spectrum radio-quasars (FSRQs) and eight BL Lac objects. Each AGN was observed for a time-span of ∼4 h in the R band to measure polarization and variability. Using statistical methods, we determine duty cycles for polarized emission and polarization intranight variability. We find clear differences between the two samples. A majority of the radio-loud AGN show moderate to high degrees of polarization, more than half of them also show variability in polarization. There seems to be a dividing line for polarization intranight variability at P∼ 5 per cent over which all objects vary in polarization. We did not find clear correlations between the strength of the variability and the redshift or degree of polarization. Only two out of 12 RQQs show polarized emission, both at levels of P < 1 per cent. The lack of polarization intranight variability in radio-quiet AGN points towards accretion instabilities being the cause for intranight flux variability whereas the high duty cycle of polarization variability in radio-loud objects is more likely caused by instabilities in the jet or changes of physical conditions in the jet plasma. We were able to constrain the time-scale of the detected variations to >4 h. Further studies of intranight polarization variability will be necessary to reveal exact physical conditions behind this phenomenon.
Abstract
Active galactic nuclei (AGNs), particularly the most luminous AGNs, are commonly assumed to be triggered through major mergers; however, observational evidence for this scenario is mixed. To ...investigate any influence of galaxy mergers on AGN triggering and luminosities through cosmic time, we present a sample of 106 luminous X-ray-selected type 1 AGNs from the COSMOS survey. These AGNs occupy a large redshift range (0.5 < z < 2.2) and two orders of magnitude in X-ray luminosity (∼1043–1045 erg s−1). AGN hosts are carefully mass and redshift matched to 486 control galaxies. A novel technique for identifying and quantifying merger features in galaxies is developed, subtracting galfit galaxy models and quantifying the residuals. Comparison to visual classification confirms this measure reliably picks out disturbance features in galaxies. No enhancement of merger features with increasing AGN luminosity is found with this metric, or by visual inspection. We analyse the redshift evolution of AGNs associated with galaxy mergers and find no merger enhancement in lower redshift bins. Contrarily, in the highest redshift bin (z ∼ 2) AGNs are ∼4 times more likely to be in galaxies exhibiting evidence of morphological disturbance compared to control galaxies, at 99 per cent confidence level (∼2.4σ) from visual inspection. Since only ∼15 per cent of these AGNs are found to be in morphologically disturbed galaxies, it is implied that major mergers at high redshift make a noticeable but subdominant contribution to AGN fuelling. At low redshifts, other processes dominate and mergers become a less significant triggering mechanism.
Black hole feedback is now a standard component of galaxy formation models. These models predict that the impact of black hole activity on its host galaxy likely peaked at z = 2-3, the epoch of ...strongest star formation activity and black hole accretion activity in the Universe. We used XSHOOTER on the Very Large Telescope to measure rest-frame optical spectra of four z similar to 2.5 extremely red quasars with infrared luminosities similar to 10(47) erg s(-1). We present the discovery of very broad (full width at half max = 2600-5000 km s(-1)), strongly blueshifted (by up to 1500 km s(-1)) O III lambda 5007 angstrom emission lines in these objects. In a large sample of type 2 and red quasars, O III kinematics are positively correlated with infrared luminosity, and the four objects in our sample are on the extreme end in both O III kinematics and infrared luminosity. We estimate that at least 3 per cent of the bolometric luminosity in these objects is being converted into the kinetic power of the observed wind. Photo-ionization estimates suggest that the O III emission might be extended on a few kpc scales, which would suggest that the extreme outflow is affecting the entire host galaxy of the quasar. These sources may be the signposts of the most extreme form of quasar feedback at the peak epoch of galaxy formation, and may represent an active `blow-out' phase of quasar evolution.
Research over the past decade has shown diminishing evidence for major galaxy mergers being a dominant mechanism for the growth of supermassive black holes (BHs) in galaxies and the triggering of ...optically or X-ray-selected active galactic nuclei (AGNs). For the first time we test whether such a connection exists at least in the most "plausible" part of parameter space: the highest specific accretion rate broad-line AGNs at the peak epoch of BH activity around z = 2. To that end we analyze two samples-21 AGNs with L/Ledd > 0.7 and 92 stellar mass- and redshift-matched inactive galaxies-observed with HST/WFC3. We remove the AGN point sources from their host galaxies and avoid bias in visual classification by adding and then subtracting mock point sources to and from the comparison galaxies, producing matched residual structures for both sets. The resulting samples are joined and visually ranked according to distortion strength by 10 experts. The ensuing individual rankings are combined into a consensus sequence and from this we derive the merger fractions for both samples. With the merger fractions fm,agn = 0.24 0.09 for the AGN host galaxy sample and fm,ina = 0.19 0.04 for the inactive galaxies, we find no significant difference between the samples. This finding is consistent with previous studies for different AGN populations, and we conclude that even BH growth at the highest specific accretion rates and at the peak of cosmic AGN activity is not predominantly caused by major mergers.
Abstract
Variability selection has been proposed as a powerful tool for identifying both low-luminosity active galactic nuclei (AGN) and those with unusual spectral energy distributions. However, a ...systematic study of sources selected in such a way has been lacking. In this paper, we present the multiwavelength properties of the variability-selected AGN in GOODS-South. We demonstrate that variability selection indeed reliably identifies AGN, predominantly of low luminosity. We find contamination from stars as well as a very small sample of sources that show no sign of AGN activity, their number is consistent with the expected false positive rate. We also study the host galaxies and environments of the AGN in the sample. Disturbed host morphologies are relatively common. The host galaxies span a wide range in the level of ongoing star formation. However, massive starbursts are only present in the hosts of the most luminous AGN in the sample. There is no clear environmental preference for the AGN sample in general but we find that the most luminous AGN on average avoid dense regions while some low-luminosity AGN hosted by late-type galaxies are found near the centres of groups. AGN in our sample have closer nearest neighbours than the general galaxy population. We find no indications that major mergers are a dominant triggering process for the moderate- to low-luminosity AGN in this sample. The environments and host galaxy properties instead suggest secular processes, in particular tidal processes at first passage and minor mergers, as likely triggers for the objects studied. This study demonstrates the strength of variability selection for AGN and gives first hints at possibly triggering mechanisms for high-redshift low-luminosity AGN.
ABSTRACT
In this work, we investigate the strength and impact of ionized gas outflows within z ∼ 0.04 MaNGA galaxies. We find evidence for outflows in 322 galaxies ($12{{\ \rm per\ cent}}$ of the ...analysed line-emitting sample), 185 of which show evidence for hosting an active galactic nucleus (AGN). Most outflows are centrally concentrated with a spatial extent that scales sublinearly with Re. The incidence of outflows is enhanced at higher masses, central surface densities, and deeper gravitational potentials, as well as at higher star formation rate (SFR) and AGN luminosity. We quantify strong correlations between mass outflow rates and the mechanical drivers of the outflow of the form $\dot{M}_{\rm out} \propto \rm SFR^{0.97}$ and $\dot{M}_{\rm out} \propto L_{\rm AGN}^{0.55}$. We derive a master scaling relation describing the mass outflow rate of ionized gas as a function of M⋆, SFR, Re, and LAGN. Most of the observed winds are anticipated to act as galactic fountains, with the fraction of galaxies with escaping winds increasing with decreasing potential well depth. We further investigate the physical properties of the outflowing gas finding evidence for enhanced attenuation in the outflow, possibly due to metal-enriched winds, and higher excitation compared to the gas in the galactic disc. Given that the majority of previous studies have focused on more extreme systems with higher SFRs and/or more luminous AGN, our study provides a unique view of the non-gravitational gaseous motions within ‘typical’ galaxies in the low-redshift Universe, where low-luminosity AGN and star formation contribute jointly to the observed outflow phenomenology.
Extremely red quasars in BOSS Hamann, Fred; Zakamska, Nadia L; Ross, Nicholas ...
Monthly notices of the Royal Astronomical Society,
01/2017, Letnik:
464, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Red quasars are candidate young objects in an early transition stage of massive galaxy evolution. Our team recently discovered a population of extremely red quasars (ERQs) in the Baryon Oscillation ...Spectroscopic Survey (BOSS) that has a suite of peculiar emission-line properties including large rest equivalent widths (REWs), unusual 'wingless' line profiles, large N v/Ly..., N v/C iv, Si iv/C iv and other flux ratios, and very broad and blueshifted Oiii ...5007. Here we present a new catalogue of C iv and N v emission-line data for 216 188 BOSS quasars to characterize the ERQ line properties further. We show that they depend sharply on UV-to-mid-IR colour, secondarily on REW(C iv), and not at all on luminosity or the Baldwin Effect. We identify a 'core' sample of 97 ERQs with nearly uniform peculiar properties selected via i-W3 greater than or equal to 4.6 (AB) and REW(C iv) greater than or equal to 100 A at redshifts 2.0-3.4. A broader search finds 235 more red quasars with similar unusual characteristics. The core ERQs have median luminosity ...log L(ergs s super( -1))... ~ 47.1, sky density 0.010 deg super( -2), surprisingly flat/blue UV spectra given their red UV-to-mid-IR colours, and common outflow signatures including BALs or BAL-like features and large C iv emission-line blueshifts. Their SEDs and line properties are inconsistent with normal quasars behind a dust reddening screen. We argue that the core ERQs are a unique obscured quasar population with extreme physical conditions related to powerful outflows across the line-forming regions. Patchy obscuration by small dusty clouds could produce the observed UV extinctions without substantial UV reddening. (ProQuest: ... denotes formulae/symbols omitted.)
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