A Search for Signatures of Quasar Evolution: Comparison of the Shapes of the Rest‐Frame Optical/Ultraviolet Continua of Quasars at z > 3 and z ∼ 0.1

Near-IR photometry for 20 radio-loud z>3 quasars, 16 of which are radio- selected, are presented. These data sample the rest-frame optical/UV continuum, which is commonly interpreted as emission from an accretion disk. In a previous study, we compared the rest-frame optical/UV continuum shapes of 15 optically bright (V 3 quasars with those of 27 low redshift (z~0.1) ones that were matched to the high redshift sample in evolved luminosity (i.e. having luminosities ranging from 1-7 times the characteristic luminosity, L*, where L*~(1+z)^{~3}) to look for signs of evolution in the central engines. We found the continuum shapes at z~0.1 and z>3 similar, consistent with no significant change in the ratio mdot/M, where mdot is the accretion rate with respect to the Eddington rate and M is the black hole mass. This study expands our earlier high redshift sample to lower luminosity, away from extreme objects and towards a luminosity overlap with lower redshift samples. The distribution of rest-frame optical/UV continuum shapes for this fainter sample is broader, extending further to the red than that of the brighter z>3 one. Three quasars from this fainter sample, two radio-selected and one optically-selected, have optical continuum slopes alpha<-1 (F_{nu}~nu^{alpha}). The optically-selected one, LBQS0056+0125, appears to be reddened by dust along the line of sight or in the host galaxy, whereas the radio-selected ones, PKS2215+02 and TXS2358+189, could derive their red continua from the contribution of a relatively strong synchrotron component to the rest-frame optical. These objects may represent a bridge to a population of very red high redshift quasars to which ongoing or future near-IR, optical and deep X-ray surveys will be sensitive.

Recent high redshift surveys for 21-cm absorption in damped Lyman-alpha absorption systems (DLAs) take the number of published searches at z > 2 to 25, the same number as at z < 2, although the detection rate at high redshift remains significantly lower (20% cf. 60%). Using the known properties of the DLAs to estimate the unknown profile widths of the 21-cm non-detections and including the limits via a survival analysis, we show that the mean spin temperature/covering factor degeneracy at high redshift is, on average, double that of the low redshift sample. This value is significantly lower than the previous factor of eight for the spin temperatures and is about the same factor as in the angular diameter distance ratios between the low and high redshift samples. That is, without the need for the several pivotal assumptions, which lead to an evolution in the spin temperature, we show that the observed distribution of 21-cm detections in DLAs can be accounted for by the geometry effects of an expanding Universe. That is, as yet there is no evidence of the spin temperature of gas rich galaxies evolving with redshift.

We previously reported Keck telescope observations suggesting a smaller value of the fine structure constant α at high redshift. New Very Large Telescope (VLT) data, probing a different direction in the Universe, shows an inverse evolution; α increases at high redshift. Although the pattern could be due to as yet undetected systematic effects, with the systematics as presently understood the combined data set fits a spatial dipole, significant at the 4.2 σ level, in the direction right ascension 17.5 ± 0.9 h, declination -58 ± 9 deg. The independent VLT and Keck samples give consistent dipole directions and amplitudes, as do high and low redshift samples. A search for systematics, using observations duplicated at both telescopes, reveals none so far which emulate this result.

Context. Despite the increasing prevalence of radio-loud (RL) sources at cosmic noon, our understanding of the underlying physics that governs the accretion disc outflows in these particular sources and its dissimilarity with radio-quiet (RQ) quasars remains somewhat limited. Aims. Disentangling the real impact of the radio-loudness and accretion on the outflow parameters remains a challenge to this day. We present ten new spectra of high-redshift and high-luminosity quasars and combine these with previous data at both high and low redshift with the aim being to evaluate the role of the feedback from RL and RQ AGN. The final high-redshift (1.5 ≲ z ≲ 3.9), high-luminosity (47.1 ≤ log(L) ≤ 48.5) sample consists of a combination of 60 quasars from our ISAAC and the Hamburg-ESO surveys. The low-redshift (z ≤ 0.8) sample has 84 quasars that have been analyzed in the optical and with the Faint Object Spectrograph (FOS) data in the UV. Methods. We perform a multicomponent analysis of optical and UV emission line profiles along the quasar main sequence, and provide a relation that can be used to estimate the main outflow parameters (mass rate, thrust, and kinetic power) in both the BLR and NLR through the analysis of the [O III]λ5007 and C IVλ1549 emission lines. Results. Spectrophotometric properties and line profile measurements are presented for Hβ+[O III]λλ4959,5007, Si IVλ1397+O IV]λ1402, C IVλ1549+He IIλ1640, and the 1900 Å blend. High-ionization lines, such as C IVλ1549 and [O III]λ5007, usually present a significant asymmetry toward the blue, especially in radio-quiet sources. This is strong evidence of outflow motions. In the ISAAC sample, 72% of the quasars where [O III] is clearly detected present significant outflows, with centroid velocity at half intensity blueshifted to values of greater than ∼250 km s−1. Radio-loud quasars tend to present slightly more modest blueshifted components in both the UV and optical ranges. The behavior of [O III]λ5007 mirrors that of C IVλ1549, with blueshift amplitudes between the two lines showing a high degree of correlation, which appears unaffected by the presence of radio emission. Conclusions. In contrast to the situation at low redshift, both RL and RQ AGN outflow parameters at high luminosity appear in the range needed to provide feedback effects on their host galaxies. Both high- and low-z RL quasars exhibit smaller outflows compared to RQ quasars, suggesting a potential role of radio-loudness in mitigating outflow effects. Nevertheless, the radio-loudness effect on AGN feedback is much less significant than the effect of accretion, with this latter emerging as the main driver of nuclear outflows.

Gamma-ray bursts (GRBs) are the most energetic events after the Big Bang and they have been observed up to very high redshift. By means of measures of chemical abundances now available for the galaxies hosting such events,thought to originate from the explosion of very powerful supernovae (Type Ib/c), we have the opportunity to study the nature of these host galaxies. The aim of this paper is to identify the hosts of Long GRBs (LGRBs) observed both at low and high redshift to see whether the hosts can be galaxies of the same type observed at different cosmic epochs. We adopt detailed chemical evolution models for galaxies of different morphological type (ellipticals, spirals, irregulars) which follow the time evolution of the abundances of several chemical elements (H, He, $\alpha$-elements, Fe), and compare the results with the observed abundances and abundance ratios in galaxies hosting LGRBs. We find that the abundances and abundance ratios predicted by models devised for typical irregular galaxies can well fit the abundances in the hosts both at high and low redshift. We also find that the predicted Type Ib/c supernova rate for irregulars is in good agreement with observations. Models for spirals and particularly ellipticals do not fit the high-redshift hosts of LGRBs (DLA systems) nor the low redshift hosts: in particular, ellipticals cannot possibly be the hosts of gamma-ray-bursts at low redshift since they do not show any star formation, and therefore no supernovae Ib/c. We conclude that the observed abundance and abundance ratios in LGRBs hosts suggest that these hosts are irregular galaxies both at high and low redshift thus showing that the host galaxies belong to in an evolutionary sequence.

We present spectra for 14 high-redshift (0.17 < z < 0.83) supernovae, which were discovered by the Supernova Cosmology Project as part of a campaign to measure cosmological parameters. The spectra are used to determine the redshift and classify the supernova type, essential information if the supernovae are to be used for cosmological studies. Redshifts were derived either from the spectrum of the host galaxy or from the spectrum of the supernova itself. We present evidence that these supernovae are of Type Ia by matching to spectra of nearby supernovae. We find that the dates of the spectra relative to maximum light determined from this fitting process are consistent with the dates determined from the photometric light curves, and moreover the spectral time-sequence for SNe Type Ia at low and high redshift is indistinguishable. We also show that the expansion velocities measured from blueshifted CaHK are consistent with those measured for low-redshift Type Ia supernovae. From these first-level quantitative comparisons we find no evidence for evolution in SNIa properties between these low- and high-redshift samples. Thus even though our samples may not be complete, we conclude that there is a population of SNe Ia at high redshift whose spectral properties match those at low redshift.

We use the distributions of spectral indices (α v ) of a large homogenous sample of Fermi-detected blazars to re-investigate the relationship between flat spectrum radio quasars (FSRQs) and subclasses of BL Lac objects (BL Lacs). We compute the broadband synchrotron and Compton spectral indices from radio-to-X-ray and X-ray to y-ray bands, respectively. Analyses of our data show continuity in the distributions of the spectral indices from FSRQs to HSP through LSP and ISP subclasses of BL Lacs. We find from y-ray luminosity distribution that the jetted radio galaxies form the low-luminosity tail of the distribution, which is suggestive that the sequence can be extended to the young jetted galaxy populations. We observe a significant difference in the shape of Compton and synchrotron spectra: significant anti-correlation (r ∼−0.80) exists between the broadband Compton and synchrotron spectral indices. Furthermore, the broadband spectral indices vary significantly with redshift (z) at low redshift (z &lt; 0.3) and remain fairly constant at high (z ≥ 0.3) redshift. The trend of the variations suggests a form of evolutionary connection between subclasses of blazars. Thus, while selection effect may be significant at low redshift, evolutionary sequence can also be important. Our results are not only consistent with a unified scheme for blazars and their young jetted galaxy counterparts but also suggest that the broadband spectral sequence of blazars is not a secondary effect of redshift dependence.

Context. The detection and follow-up observations of high-redshift (z &gt; 6) gamma-ray bursts (GRBs) provide a unique opportunity to explore the properties of the distant Universe. Unfortunately, they are rather rare, with only a dozen of them identified so far. Aims. We present here the discovery of the GRB with the second highest spectroscopic redshift measured to date, GRB 240218A at z = 6.782, and the broadband analysis of its afterglow. Following the detection by high-energy satellites, we obtained multi-epoch and multi-wavelength photometric follow-up observations, from 68 s to ∼48 d after the detection. These data allow us to perform a comprehensive study of the emission and physical properties of this event. We also compare these properties with GRBs observed at high and low redshift. Methods. We built the X-ray, near-infrared, and radio light curves and studied their temporal evolution. Moreover, we investigated the spectral energy distribution (SED) at different times to trace possible spectral evolution. We also compared the prompt phase properties, X-ray luminosity, and optical extinction of GRB 240218A with those of the long-duration GRB (LGRB) population. Results. The SED analysis reveals a typical afterglow-like behaviour at late times. The origin of the early-time emission is uncertain, with the probable presence of an additional contribution on top of the afterglow emission. From the broadband physical modelling of the afterglow, we identify a narrow Gaussian jet seen slightly off-axis, θv = 2.52−0.29+0.57 deg, and pinpoint the presence of a possible jet break ∼0.86 d after the trigger. Conclusions. The results of the analysis and the comparison with other high-z GRBs reveal that we can consider GRB 240218A as a ‘standard’ high-redshift LGRB: the prompt phase properties, the X-ray luminosity, and the optical extinction are consistent with the values derived for the LGRB population. The jet opening angle is narrower but compatible with those of high-z bursts, possibly pointing to more collimated jets at high redshift.

view Abstract Citations (60) References (119) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared to X-Ray Spectral Energy Distributions of High Redshift Quasars Bechtold, Jill ; Elvis, Martin ; Fiore, Fabrizio ; Kuhn, Olga ; Cutri, Roc M. ; McDowell, Jonathan C. ; Rieke, Marcia ; Siemiginowska, Aneta ; Wilkes, Belinda J. Abstract We have observed 14 quasars with z > 2.8 with the ROSAT-PSPC, and detected 12 of them, including the z = 4.11 quasar 0000-263. We present the first x-ray spectrum of a radio quiet quasar with z > 3, 1946+768. Its x-ray spectrum is consistent with a power law with spectral index α_E_= 1.8_-1.4_^+2.1^ and no evidence for absorption in excess of the galactic column [α_E_ = 1.00_-0.32_^+0.28^ assuming N_H_ = N_H_(Gal)]. A PSPC hardness ratio is used to constrain the x-ray spectral properties of the quasars for which there were less than 100 photons detected. For the radio quiet quasars, <α_E_> ~ 1.2, if one assumes that there is no absorption in excess of the galactic column. We combine the x-ray data with new ground based optical and near-IR spectrophotometry obtained at the Steward 23 m and Multiple Mirror Telescope, and data from the literature. The spectral energy distributions are compared to those of low redshift objects. For the radio quiet quasars with z > 2.5, the mean <α_ox_>~1.8. This is larger than the mean for quasars with z < 2.5, but consistent with the expected value for quasars with the high optical luminosities of the objects in this sample. For the radio-loud quasars, <α_ox_>~1.4, independent of redshift. This is smaller than the expected value for the optically luminous, high redshift objects in this sample, if they are mostly GHz peaked radio sources and hence comparable to steep-spectrum, compact radio sources at lower redshift. Finally, we compare the spectral energy distributions of two representative objects to the predicted spectrum of a thin accretion disk in the Kerr geometry, and discuss the uncertainties in deriving black hole masses and mass accretion rates. Publication: The Astronomical Journal Pub Date: August 1994 DOI: 10.1086/117076 Bibcode: 1994AJ....108..374B Keywords: Astronomical Spectroscopy; Infrared Astronomy; Quasars; Red Shift; Spectral Energy Distribution; X Ray Spectroscopy; Accretion Disks; Galaxies; Infrared Photometry; Radio Astronomy; Spectrophotometry; X Ray Astronomy; Astrophysics; INFRARED: GALAXIES; RADIO CONTINUUM: GALAXIES; ULTRAVIOLET: GALAXIES; X-RAYS: GALAXIES; QUASARS: EMISSION LINES full text sources ADS | data products SIMBAD (21) NED (21)

We present the results of a multi-wavelength study of a sample of high-redshift Radio Loud (RL) Broad Absorption Line (BAL) quasars. This way we extend to higher redshift previous studies on the radio properties, and broadband optical colors of these objects. We have se- lected a sample of 22 RL BAL quasars with 3.6 z 4.8 cross-correlating the FIRST radio survey with the SDSS. Flux densities between 1.25 and 9.5 GHz have been collected with the JVLA and Effelsberg-100m telescopes for 15 BAL and 14 non-BAL quasars used as compar- ison sample. We determine the synchrotron peak frequency, constraining their age. A large number of GigaHertz Peaked Spectrum (GPS) and High Frequency Peakers (HFP) sources has been found in both samples (80% for BAL and 71% for non-BAL QSOs), not suggesting a younger age for BAL quasars. The spectral index distribution provides information about the orientation of these sources, and we find statistically similar distributions for the BAL and non-BAL quasars in contrast to work done on lower redshift samples. Our sample may be too small to convincingly find the same effect, or might represent a real evolutionary effect based on the large fraction of young sources. We also study the properties of broadband colors in both optical (SDSS) and near- and mid-infrared (UKIDSS and WISE) bands, finding that also at high redshift BAL quasars tend to be optically redder than non-BAL quasars. However, these differences are no more evident at longer wavelength, when comparing colors of the two samples by mean of the WISE survey.

We use the results of the SCUBA Local Universe Galaxy Survey, a submillimetre survey of galaxies in the nearby Universe, to investigate the relationship between the far-infrared--submillimetre and radio emission of galaxies at both low and high redshift. At low redshift we show that the correlation between radio and far-infrared emission is much stronger than the correlation between radio and submillimetre emission, which is evidence that massive stars are the source of both the far-infrared and radio emission. At high redshift we show that the submillimetre sources detected by SCUBA are brighter sources of radio emission than are predicted from the properties of galaxies in the local Universe. We discuss possible reasons for the cosmic evolution of the relationship between radio and far-infrared emission.

Using archival data of low-redshift (z < 0.01) Type Ia supernovae (SN Ia) and recent observations of high-redshift (0.16 < z <0.64; Matheson et al. 2005) SN Ia, we study the "uniformity'' of the spectroscopic properties of nearby and distant SN Ia. We find no difference in the measures we describe here. In this paper, we base our analysis solely on line-profile morphology, focusing on measurements of the velocity location of maximum absorption (vabs) and peak emission (vpeak). We find that the evolution of vabs and vpeak for our sample lines (Ca II 3945, Si II 6355, and S II 5454, 5640) is similar for both the low- and high-redshift samples. We find that vabs for the weak S II 5454, 5640 lines, and vpeak for S II 5454, can be used to identify fast-declining [dm15 > 1.7] SN Ia, which are also subluminous. In addition, we give the first direct evidence in two high-z SN Ia spectra of a double-absorption feature in Ca II 3945, an event also observed, though infrequently, in low-redshift SN Ia spectra (6/22 SN Ia in our local sample). We report for the first time the unambiguous and systematic intrinsic blueshift of peak emission of optical P-Cygni line profiles in Type Ia spectra, by as much as 8000 km/s. All the high-z SN Ia analyzed in this paper were discovered and followed up by the ESSENCE collaboration, and are now publicly available.

The inflationary ΛCDM cosmology currently provides an accurate description of the Universe. It has been tested using several observational techniques over a wide redshift range, and it provides a good fit to most of them. In addition, it is a surprisingly economical model, requiring only six parameters to characterize the background cosmology and its fluctuations. In this model, the Universe is dominated by a cosmological constant Λ driving an accelerated expansion, and by cold dark matter. The strongest constraints on parameters to date come from observations of the temperature and polarization anisotropies of the cosmic microwave background measured by the Planck satellite. There are, however, indications of features in the Planck power spectra, possible differences with high redshift ground-based CMB experiments, and ‘tensions’ between Planck and low redshift measurements of the Hubble constant and weak gravitational lensing.In this thesis, we review possible tensions and extensions to the Planck cosmology, at both high and low redshifts. We begin with the high redshift analysis, using the Planck data to test models which introduce oscillatory features in the primordial power spectrum. We also study possible departures from slow roll inflation using the generalized slow-roll formalism, which allows for order unity deviations. Although we find models which give marginal improvements on the temperature or polarization power spectra, the combination of temperature and polarization is found to be consistent with a featureless power-law primordial spectrum. We then focus on measurements of the polarized CMB sky by the South Pole Telescope collaboration, who report tension between their measurements and the ΛCDM cosmology and with the cosmological parameters determined by Planck. We find evidence of a high χ2 in the SPTpol spectra which is unlikely to be cosmological. We report consistency between the Planck and SPTpol polarization spectra over the multipoles accessible to Planck (l ∼< 1500).We then investigate tension at low redshifts. We begin with weak gravitational lensing in which a number of surveys have suggested that the amplitude of the fluctuation spectra is lower than the Planck value. We review the small-angle approximations commonly used in galaxy weak lensing analyses and their effect on cosmological parameters. We find that these approximations are perfectly adequate for present and near future experiments. We find internal inconsistencies in the recent KiDS-450 analysis involving photometric redshifts and the KiDS covariance matrix at large scales. Finally, we investigate the difference between measurements of the present day expansion rate of the Universe. We apply a novel parameterization of the inverse distance ladder to determine the present date value of the Hubble parameter H0, which assumes General Relativity but makes no further assumptions about systematic errors or the nature of dark energy. Our analysis uses baryon acoustic oscillation data and Type Ia Supernovae to constrain the expansion history assuming a value of the sound horizon determined from the CMB. Our results are in tension with recent direct determinations of H0. We conclude that this tension, if real, cannot be solved by modifications of the ΛCDM model at late times. Instead, we would require a modification of the theory at early times which reduces the sound horizon.We conclude that at this time there is no compelling evidence that conflicts with the ΛCDM cosmology either at low or at high redshifts.

In this paper, we investigate the possible reasons why H i 21-cm absorption in damped Lyman α systems (DLAs) has only been detected at low redshift. To date, no 21-cm absorption has yet been detected at zabs > 2.3, and at redshifts less than this, there is a mix of detections and non-detections in the DLAs searched. This has been attributed to the morphologies of the galaxies hosting the DLAs, where at low redshift the DLAs comprise both large and compact galaxies, which are believed to have low and high spin temperatures, respectively. Likewise, at high redshift the DLA population is believed to consist exclusively of compact galaxies of high spin temperature. However, in a previous paper, we found that by not assuming or assigning an often uncertain value for the coverage of the radio continuum source by the 21-cm absorbing gas, that there is generally no difference in the spin temperature/covering factor ratio between the 21-cm detections and non-detections or between the low- and high-redshift samples. Furthermore, only one of the 18 non-detections has a known host morphology, thus making any link between morphology and 21-cm delectability highly speculative. We suggest that the lack of 21-cm absorption detections at high redshift arises from the fact that these DLAs are at similar angular diameter distances to the background quasars (i.e. the distance ratios are always close to unity). Above zabs∼ 1.6, the covering factor becomes largely independent of the DLA–QSO distance, making the high-redshift absorbers much less effective at covering the background continuum emission. At low redshift, small distance ratios are strongly favoured by the 21-cm detections, whereas large ratios are favoured by the non-detections. This mix of distance ratios gives the observed mix of detections and non-detections at zabs≲ 1.6. In addition to the predominance of large distance ratios and non-detections at high redshift, this strongly suggests that the observed distribution of 21-cm absorption in DLAs is dominated by geometric effects.

The detection of powerful near-infrared emission in high redshift (z > 5) quasars demonstrates that very hot dust is present close to the active nucleus also in the very early universe. A number of high-redshift objects even show significant excess emission in the rest frame NIR over more local AGN spectral energy distribution (SED) templates. In order to test if this is a result of the very high luminosities or redshifts, we construct mean SEDs from the latest SDSS quasar catalogue in combination with MIR data from the WISE preliminary data release for several redshift and luminosity bins. Comparing these mean SEDs with a large sample of z > 5 quasars we could not identify any significant trends of the NIR spectral slope with luminosity or redshift in the regime 2.5 < z ≲ 6 and 1045 < νLν (1350Å) ≲ 1047 erg/s. In addition to the NIR regime, our combined Herschel and Spitzer photometry provides full infrared SED coverage of the same sample of z > 5 quasars. These observations reveal strong FIR emission (LFIR ≳ 1013 L⊙) in seven objects, possibly indicating star-formation rates of several thousand solar masses per year. The FIR excess emission has unusally high temperatures (T∼65K) which is in contrast to the temperature typically expected from studies at lower redshift (T∼45K). These objects are currently being investigated in more detail.