263 research outputs found
Physical and projected pairs of quasars.
Quasars are the most luminous type of active galactic nuclei and their study is fundamental to shed light on the high redshift Universe. In this work we take advantage of the rare cases of close projected and physical quasar pairs to detect the presence of the cool enriched gas and of the dark mass that surround quasars.
This Thesis consists of two parts. In the first one we present optical spectroscopy of projected quasar pairs (i.e., two quasars that are close in the sky but have discordant redshifts) that represents a powerful tool to investigate the metal absorption lines imprinted on the spectrum of the background quasar by the gaseous halo surrounding the foreground one (Chapter 1). In the last decades, this technique has been extensively used to detect the haloes of non–active galaxies, but to date no systematic study has been performed in the case of quasars. We selected a sample of 46 projected pairs, with separations ranging from ∼ 50 kpc to ∼ 200 kpc, aimed to assess the presence of Mg II and CIV absorptions systems associated to foreground quasars. In Chapter 2 we show the first outcomes of our programme, based on the spectra of 13 pairs partially collected by me at the ESO Very Large Telescope (VLT). These data reveal a high covering fraction for the Mg II absorbers and a non isotropical distribution of the gas. Our results are compared to those of similar works performed on non–active galaxies available in the literature. We propose that the cool gaseous haloes of quasars and of normal galaxies are similar, once the stellar mass of the systems is taken into account. Observations of the remaining 33 pairs are ongoing at the Gran Telescopio Canarias (GTC). The preparatory analysis of the SDSS spectra of these systems show that a 10m class telescope is mandatory for this kind of studies (Chapter 3).
The second part of the Thesis addresses with physical systems of quasars (i.e., two or more quasars that have small projected and redshift separations) that are an expected outcome of the current hierarchical framework of galaxy formation and evolution (Chapter 4). In Chapter 5 we accurately study the dynamics of six low redshift quasar pairs and we found that the dynamical mass required for this systems to be gravitationally bound is larger of than the stellar masses of the host galaxies. This suggests that these pairs are hosted by galaxies with massive dark haloes or that they reside in a group/cluster of galaxies. In Chapter 6, we present our discovery of the second physical quasar triplet known to date. We estimate that these systems are extremely rare in terms of simple accidental superposition of the three quasars, suggesting a possible common origin for their ignition. Finally, conclusions and future perspectives of this study are presented in Chapter 7.
The present work principally deals with the analysis and studies presented in Farina et al. (2012b, on the gaseous haloes of quasars), in Farina et al. (2011, on the dynamical study of low redshift quasar pairs), and in Farina et al. (2012c, on the discovery of a new quasar triplet). A complete list of works published during my PhD is provided in Appendix C
Physical and projected pairs of quasars.
Quasars are the most luminous type of active galactic nuclei and their study is fundamental to shed light on the high redshift Universe. In this work we take advantage of the rare cases of close projected and physical quasar pairs to detect the presence of the cool enriched gas and of the dark mass that surround quasars.
This Thesis consists of two parts. In the first one we present optical spectroscopy of projected quasar pairs (i.e., two quasars that are close in the sky but have discordant redshifts) that represents a powerful tool to investigate the metal absorption lines imprinted on the spectrum of the background quasar by the gaseous halo surrounding the foreground one (Chapter 1). In the last decades, this technique has been extensively used to detect the haloes of non\u2013active galaxies, but to date no systematic study has been performed in the case of quasars. We selected a sample of 46 projected pairs, with separations ranging from 3c 50 kpc to 3c 200 kpc, aimed to assess the presence of Mg II and CIV absorptions systems associated to foreground quasars. In Chapter 2 we show the first outcomes of our programme, based on the spectra of 13 pairs partially collected by me at the ESO Very Large Telescope (VLT). These data reveal a high covering fraction for the Mg II absorbers and a non isotropical distribution of the gas. Our results are compared to those of similar works performed on non\u2013active galaxies available in the literature. We propose that the cool gaseous haloes of quasars and of normal galaxies are similar, once the stellar mass of the systems is taken into account. Observations of the remaining 33 pairs are ongoing at the Gran Telescopio Canarias (GTC). The preparatory analysis of the SDSS spectra of these systems show that a 10m class telescope is mandatory for this kind of studies (Chapter 3).
The second part of the Thesis addresses with physical systems of quasars (i.e., two or more quasars that have small projected and redshift separations) that are an expected outcome of the current hierarchical framework of galaxy formation and evolution (Chapter 4). In Chapter 5 we accurately study the dynamics of six low redshift quasar pairs and we found that the dynamical mass required for this systems to be gravitationally bound is larger of than the stellar masses of the host galaxies. This suggests that these pairs are hosted by galaxies with massive dark haloes or that they reside in a group/cluster of galaxies. In Chapter 6, we present our discovery of the second physical quasar triplet known to date. We estimate that these systems are extremely rare in terms of simple accidental superposition of the three quasars, suggesting a possible common origin for their ignition. Finally, conclusions and future perspectives of this study are presented in Chapter 7.
The present work principally deals with the analysis and studies presented in Farina et al. (2012b, on the gaseous haloes of quasars), in Farina et al. (2011, on the dynamical study of low redshift quasar pairs), and in Farina et al. (2012c, on the discovery of a new quasar triplet). A complete list of works published during my PhD is provided in Appendix C
Circum-galactic medium in the halo of quasars
The properties of circum-galactic gas in the halo of quasar host galaxies are
investigated analyzing Mg II 2800 and C IV 1540 absorption-line systems along
the line of sight close to quasars. We used optical spectroscopy of closely
aligned pairs of quasars (projected distance 200 kpc, but at very
different redshift) obtained at the VLT and Gran Telescopio Canarias to
investigate the distribution of the absorbing gas for a sample of quasars at
z1. Absorption systems of EW 0.3 associated with the
foreground quasars are revealed up to 200 kpc from the centre of the host
galaxy, showing that the structure of the absorbing gas is patchy with a
covering fraction quickly decreasing beyond 100 kpc. In this contribution we
use optical and near-IR images obtained at VLT to investigate the relations
between the properties of the circum-galactic medium of the host galaxies and
of the large scale galaxy environments of the foreground quasars.Comment: 6 pages, 3 figures, proceedings of the conference "QUASARS at all
cosmic epochs", accepted for publication on Frontiers in Astronomy and Space
Scienc
A powerful radio-loud quasar at the end of cosmic reionization
We present the discovery of the radio-loud quasar PSO J352.4034-15.3373 at
z=5.84 pm 0.02. This quasar is the radio brightest source known, by an order of
magnitude, at z~6 with a flux density in the range of 8-100 mJy from 3GHz to
230MHz and a radio loudness parameter R>~1000. This source provides an
unprecedented opportunity to study powerful jets and radio-mode feedback at the
highest redshifts, and presents the first real chance to probe deep into the
neutral intergalactic medium by detecting 21 cm absorption at the end of cosmic
reionization.Comment: ApJL accepted on May 8, 2018. See the companion paper by Momjian et
a
Mapping the Lyman-Alpha Emission Around a z~6.6 QSO with MUSE: Extended Emission and a Companion at Close Separation
We utilize the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large
Telescope (VLT) to search for extended Lyman-Alpha emission around the z~6.6
QSO J0305-3150. After carefully subtracting the point-spread-function, we reach
a nominal 5-sigma surface brightness limit of SB = 1.9x10
erg/s/cm/arcsec over a 1 arcsec aperture, collapsing 5 wavelength
slices centered at the expected location of the redshifted Lyman-Alpha emission
(i.e. at 9256 Ang.). Current data suggest the presence (5-sigma, accounting for
systematics) of a Lyman-Alpha nebula that extends for 9 kpc around the QSO.
This emission is displaced and redshifted by 155 km/s with respect to the
location of the QSO host galaxy traced by the [CII] emission line. The total
luminosity is L = 3.0x10 erg/s. Our analysis suggests that this emission
is unlikely to rise from optically thick clouds illuminated by the ionizing
radiation of the QSO. It is more plausible that the Lyman-Alpha emission is due
to fluorescence of the highly ionized optically thin gas. This scenario implies
a high hydrogen volume density of n ~ 6 cm. In addition, we detect a
Lyman-Alpha emitter (LAE) in the immediate vicinity of the QSO: i.e., with a
projected separation of 12.5 kpc and a line-of-sight velocity difference of 560
km/s. The luminosity of the LAE is L = 2.1x10 erg/s and its inferred
star-formation-rate is SFR ~ 1.3 M/yr. The probability of finding such
a close LAE is one order of magnitude above the expectations based on the
QSO-galaxy cross-correlation function. This discovery is in agreement with a
scenario where dissipative interactions favour the rapid build-up of
super-massive black holes at early Cosmic times.Comment: 17 pages, 15 figures. Accepted for publication in Ap
Mapping the Lyman-Alpha Emission Around a z~6.6 QSO with MUSE: Extended Emission and a Companion at Close Separation
We utilize the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large
Telescope (VLT) to search for extended Lyman-Alpha emission around the z~6.6
QSO J0305-3150. After carefully subtracting the point-spread-function, we reach
a nominal 5-sigma surface brightness limit of SB = 1.9x10
erg/s/cm/arcsec over a 1 arcsec aperture, collapsing 5 wavelength
slices centered at the expected location of the redshifted Lyman-Alpha emission
(i.e. at 9256 Ang.). Current data suggest the presence (5-sigma, accounting for
systematics) of a Lyman-Alpha nebula that extends for 9 kpc around the QSO.
This emission is displaced and redshifted by 155 km/s with respect to the
location of the QSO host galaxy traced by the [CII] emission line. The total
luminosity is L = 3.0x10 erg/s. Our analysis suggests that this emission
is unlikely to rise from optically thick clouds illuminated by the ionizing
radiation of the QSO. It is more plausible that the Lyman-Alpha emission is due
to fluorescence of the highly ionized optically thin gas. This scenario implies
a high hydrogen volume density of n ~ 6 cm. In addition, we detect a
Lyman-Alpha emitter (LAE) in the immediate vicinity of the QSO: i.e., with a
projected separation of 12.5 kpc and a line-of-sight velocity difference of 560
km/s. The luminosity of the LAE is L = 2.1x10 erg/s and its inferred
star-formation-rate is SFR ~ 1.3 M/yr. The probability of finding such
a close LAE is one order of magnitude above the expectations based on the
QSO-galaxy cross-correlation function. This discovery is in agreement with a
scenario where dissipative interactions favour the rapid build-up of
super-massive black holes at early Cosmic times.Comment: 17 pages, 15 figures. Accepted for publication in Ap
Copious Amounts of Dust and Gas in a z=7.5 Quasar Host Galaxy
We present IRAM/NOEMA and JVLA observations of the quasar J1342+0928 at
z=7.54 and report detections of copious amounts of dust and [CII] emission in
the interstellar medium (ISM) of its host galaxy. At this redshift, the age of
the universe is 690 Myr, about 10% younger than the redshift of the previous
quasar record holder. Yet, the ISM of this new quasar host galaxy is
significantly enriched by metals, as evidenced by the detection of the [CII]
158micron cooling line and the underlying far-infrared (FIR) dust continuum
emission. To the first order, the FIR properties of this quasar host are
similar to those found at a slightly lower redshift (z~6), making this source
by far the FIR-brightest galaxy known at z>7.5. The [CII] emission is spatially
unresolved, with an upper limit on the diameter of 7 kpc. Together with the
measured FWHM of the [CII] line, this yields a dynamical mass of the host of
<1.5x10^11 M_sun. Using standard assumptions about the dust temperature and
emissivity, the NOEMA measurements give a dust mass of (0.6-4.3)x10^8 M_sun.
The brightness of the [CII] luminosity, together with the high dust mass, imply
active ongoing star formation in the quasar host. Using [CII]-SFR scaling
relations, we derive star formation rates of 85-545 M_sun/yr in the host,
consistent with the values derived from the dust continuum. Indeed, an episode
of such past high star formation is needed to explain the presence of ~10^8
M_sun of dust implied by the observations.Comment: 8 pages, 4 figures. Published in ApJ Letter
A metal-poor damped Ly-alpha system at redshift 6.4
We identify a strong Ly-alpha damping wing profile in the spectrum of the
quasar P183+05 at z=6.4386. Given the detection of several narrow metal
absorption lines at z=6.40392, the most likely explanation for the absorption
profile is that it is due to a damped Ly-alpha system. However, in order to
match the data a contribution of an intergalactic medium 5-38% neutral or
additional weaker absorbers near the quasar is also required. The absorption
system presented here is the most distant damped Ly-alpha system currently
known. We estimate an HI column density (cm),
metallicity ([O/H]), and relative chemical abundances of a
system consistent with a low-mass galaxy during the first Gyr of the universe.
This object is among the most metal-poor damped Ly-alpha systems known and,
even though it is observed only ~850 Myr after the big bang, its relative
abundances do not show signatures of chemical enrichment by Population III
stars.Comment: Updated to match published versio
Ly Halos Around Quasars
We present deep MUSE observations of five quasars within the first Gyr of the
Universe (), four of which display extended Ly halos. After
PSF-subtraction, we reveal halos surrounding two quasars for the first time, as
well as confirming the presence of two more halos for which tentative
detections exist in long-slit spectroscopic observations and narrow-band
imaging. The four Ly halos presented here are diverse in morphology and
size, they each display spatial asymmetry, and none are centred on the position
of the quasar. Spectra of the diffuse halos demonstrate that none are
dramatically offset in velocity from the systemic redshift of the quasars
( v kms), however each halo shows a broad Ly
line, with a velocity width of order kms. Total Ly
luminosities range between erg s and erg s, reaching maximum radial extents of pkpc
from the quasar positions. We find larger sizes and higher Ly
luminosities than previous literature results at this redshift, but find no
correlation between the quasar properties and the Ly halo, suggesting
that the detected emission is most closely related to the physical properties
of the circum-galactic mediumComment: 19 pages, Accepted for publication in Ap
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