122 research outputs found
A ~6 Mpc overdensity at z = 2.7 detected along a pair of quasar sight lines: filament or protocluster?
Simulations predict that gas in the intergalactic medium (IGM) is distributed
in filamentary structures that connect dense galaxy clusters and form the
cosmic web. These structures of predominantly ionized hydrogen are difficult to
observe directly due to their lack of emitting regions. We serendipitously
detected an overdensity of log N(HI) > 18.0 absorbers at z = 2.69 along the
lines of sight toward a pair of background quasars. Three main absorption
regions spanning ~2000 km/s (corresponding to 6.4 (h_70)^(-1) Mpc proper) are
coincident in the two lines of sight, which are separated by ~90 (h_70)^(-1)
kpc transverse proper distance. Two regions have [Fe/H] < -1.9 and correspond
to mild overdensities in the IGM gas. The third region is a sub-DLA with [Fe/H]
= -1.1 that is probably associated with a galaxy. We discuss the possibility
that the lines of sight probe along the length of a filament or intercept a
galaxy protocluster
Extended Ly emission around quasars with eclipsing damped Ly systems
We present spectroscopic observations of six high redshift (
2) quasars, which have been selected for their Lyman (Ly)
emission region being only partially covered by a strong proximate ( ) coronagraphic damped Ly system (DLA). We
detected spatially extended Ly emission envelopes surrounding these six
quasars, with projected spatial extent in the range 26
51 kpc. No correlation is found between the quasar ionizing luminosity
and the Ly luminosity of their extended envelopes. This could be
related to the limited covering factor of the extended gas and/or due to the
AGN being obscured in other directions than towards the observer. Indeed, we
find a strong correlation between the luminosity of the envelope and its
spatial extent, which suggests that the envelopes are probably ionized by the
AGN. The metallicity of the coronagraphic DLAs is low and varies in the range
1.75 [Si/H] 0.63. Highly ionized gas is observed to be associated
with most of these DLAs, probably indicating ionization by the central AGN. One
of these DLAs has the highest AlIII/SiII ratio ever reported for any
intervening and/or proximate DLA. Most of these DLAs are redshifted with
respect to the quasar, implying that they might represent infalling gas
probably accreted onto the quasar host galaxies through filaments.Comment: Accepted for publication in MNRAS, 27 pages, 19 figures, 6 table
Detection of emission lines from z ~ 3 DLAs towards the QSO J2358+0149
Using VLT/X-shooter we searched for emission line galaxies associated to four
damped Lyman- systems (DLAs) and one sub-DLA at 2.73<=z<=3.25 towards
QSO J2358+0149. We detect [O III] emission from a "low-cool" DLA at z_abs =
2.9791 (having log N(HI)=21.69+\-0.10, [Zn/H] = -1.83+\-0.18) at an impact
parameter of, ~12 kpc. The associated galaxy is compact with a dynamical
mass of (1-6)x10^9 M_solar, very high excitation ([O III]/[O II] and [O
III]/[H] both greater than 10), 12+[O/H]<=8.5 and moderate star
formation rate (SFR <=2 M_solar yr^{-1}). Such properties are typically seen in
the low-z extreme blue compact dwarf galaxies. The kinematics of the gas is
inconsistent with that of an extended disk and the gas is part of either a
large scale wind or cold accretion. We detect Ly emission from the
z_abs = 3.2477 DLA (having log N(HI)=21.12+\-0.10 and [Zn/H]=-0.97+\-0.13).The
Ly emission is redshifted with respect to the metal absorption lines by
320 km s^{-1}, consistent with the location of the red hump expected in
radiative transport models. We derive SFR ~0.2-1.7 M_solar yr^{-1} and
Ly escape fraction of >=10 per cent. No other emission line is detected
from this system. Because the DLA has a small velocity separation from the
quasar (~500 km s^{-1}) and the DLA emission is located within a small
projected distance ( kpc), we also explore the possibility that the
Ly emission is being induced by the QSO itself. QSO induced Ly
fluorescence is possible if the DLA is within a physical separation of 340 kpc
to the QSO. Detection of stellar continuum light and/or the oxygen emission
lines would disfavor this possibility. We do not detect any emission line from
the remaining three systems.Comment: 13 pages, 7 figures, 4 tables (3 pages, 5 figures, 5 tables in
Appendix). Accepted for publication in MNRA
Quasars with PV broad absorption in BOSS data release 9
Broad absorption lines (BALs) found in a significant fraction of quasar
spectra identify high-velocity outflows that might be present in all quasars
and could be a major factor in feedback to galaxy evolution. Understanding the
nature of these flows requires further constraints on their physical
properties, including their column densities, for which well-studied BALs, such
as CIV 1548,1551, typically provide only a lower limit because of saturation
effects. Low-abundance lines, such as PV 1118,1128, indicate large column
densities, implying outflows more powerful than measurements of CIV alone would
indicate. We search through a sample of 2694 BAL quasars from the SDSS-III/BOSS
DR9 quasar catalog for such absorption, and we identify 81 `definite' and 86
`probable' detections of PV broad absorption, yielding a firm lower limit of
3.0-6.2% for the incidence of such absorption among BAL quasars. The
PV-detected quasars tend to have stronger CIV and SiIV absorption, as well as a
higher incidence of LoBAL absorption, than the overall BAL quasar population.
Many of the PV-detected quasars have CIV troughs that do not reach zero
intensity (at velocities where PV is detected), confirming that the outflow gas
only partially covers the UV continuum source. PV appears significantly in a
composite spectrum of non-PV-detected BAL quasars, indicating that PV
absorption (and large column densities) are much more common than indicated by
our search results. Our sample of PV detections significantly increases the
number of known PV detections, providing opportunities for follow-up studies to
better understand BAL outflow energetics.Comment: 18 pages, 12 figures. All spectral plots available at
http://www.dancapellupo.com/boss-pv-bal-spectral-plots.htm
Cold gas and a Milky Way-type 2175 {\AA} bump in a metal-rich and highly depleted absorption system
We report the detection of a strong Milky Way-type 2175 \AA extinction
bump at = 2.1166 in the quasar spectrum towards SDSS J121143.42+083349.7
from the Sloan Digital Sky Survey (SDSS) Data Release 10. We conduct follow up
observations with the Echelle Spectrograph and Imager (ESI) onboard the Keck-II
telescope and the Ultraviolet and Visual Echelle Spectrograph (UVES) on the
VLT. This 2175 \AA absorber is remarkable in that we simultaneously detect
neutral carbon (C I), neutral chlorine (Cl I), and carbon monoxide (CO). It
also qualifies as a damped Lyman alpha system. The J1211+0833 absorber is found
to be metal-rich and has a dust depletion pattern resembling that of the Milky
Way disk clouds. We use the column densities of the C I fine structure states
and the C II/C I ratio (under the assumption of ionization equilibrium) to
derive the temperature and volume density in the absorbing gas. A Cloudy
photoionization model is constructed, which utilizes additional atoms/ions to
constrain the physical conditions. The inferred physical conditions are
consistent with a canonical cold (T 100 K) neutral medium with a high
density ((H I) 100 cm) and a slightly higher pressure than the
local interstellar medium. Given the simultaneous presence of C I, CO, and the
2175 \AA bump, combined with the high metallicity, high dust depletion level
and overall low ionization state of the gas, the absorber towards J1211+0833
supports the scenario that the presence of the bump requires an evolved stellar
population.Comment: 18 pages, 17 figures, to be published in MNRA
Constraint on the time variation of the fine-structure constant with the SDSS-III/BOSS DR12 quasar sample
From the Sloan Digital Sky Survey (SDSS) Data Release 12, which covers the
full Baryonic Oscillation Spectroscopic Survey (BOSS) footprint, we investigate
the possible variation of the fine-structure constant over cosmological
time-scales. We analyse the largest quasar sample considered so far in the
literature, which contains 13175 spectra (10363 from SDSS-III/BOSS DR12 + 2812
from SDSS-II DR7) with redshift 1. We apply the emission-line method on
the [O III] doublet (4960, 5008 A) and obtain for the relative variation of the fine-structure
constant. We also investigate the possible sources of systematics:
misidentification of the lines, sky OH lines, H and broad line
contamination, Gaussian and Voigt fitting profiles, optimal wavelength range
for the Gaussian fits, chosen polynomial order for the continuum spectrum,
signal-to-noise ratio and good quality of the fits. The uncertainty of the
measurement is dominated by the sky subtraction. The results presented in this
work, being systematics limited, have sufficient statistics to constrain
robustly the variation of the fine-structure constant in redshift bins ( 0.06) over the last 7.9 Gyr. In addition, we study the [Ne III]
doublet (3870, 3969 A) present in 462 quasar spectra and discuss the systematic
effects on using these emission lines to constrain the fine-structure constant
variation. Better constraints on (10) using
the emission-line method would be possible with high-resolution spectroscopy
and large galaxy/qso surveys.Comment: 16 pages, 16 figures. Version published in MNRAS. Analysis enlarged,
public catalogue now availabl
The large-scale Quasar-Lyman \alpha\ Forest Cross-Correlation from BOSS
We measure the large-scale cross-correlation of quasars with the Lyman
\alpha\ forest absorption in redshift space, using ~ 60000 quasar spectra from
Data Release 9 (DR9) of the Baryon Oscillation Spectroscopic Survey (BOSS). The
cross-correlation is detected over a wide range of scales, up to comoving
separations r of 80 Mpc/h. For r > 15 Mpc/h, we show that the cross-correlation
is well fitted by the linear theory prediction for the mean overdensity around
a quasar host halo in the standard \Lambda CDM model, with the redshift
distortions indicative of gravitational evolution detected at high confidence.
Using previous determinations of the Lyman \alpha\ forest bias factor obtained
from the Lyman \alpha\ autocorrelation, we infer the quasar bias factor to be
b_q = 3.64^+0.13_-0.15 at a mean redshift z=2.38, in agreement with previous
measurements from the quasar auto-correlation. We also obtain a new estimate of
the Lyman \alpha\ forest redshift distortion factor, \beta_F = 1.1 +/- 0.15,
slightly larger than but consistent with the previous measurement from the
Lyman \alpha\ forest autocorrelation. The simple linear model we use fails at
separations r < 15 Mpc/h, and we show that this may reasonably be due to the
enhanced ionization due to radiation from the quasars. We also provide the
expected correction that the mass overdensity around the quasar implies for
measurements of the ionizing radiation background from the line-of-sight
proximity effect.Comment: 24 pages, 6 figures, published in JCA
Characterizing unknown systematics in large scale structure surveys
Photometric large scale structure (LSS) surveys probe the largest volumes in
the Universe, but are inevitably limited by systematic uncertainties. Imperfect
photometric calibration leads to biases in our measurements of the density
fields of LSS tracers such as galaxies and quasars, and as a result in
cosmological parameter estimation. Earlier studies have proposed using
cross-correlations between different redshift slices or cross-correlations
between different surveys to reduce the effects of such systematics. In this
paper we develop a method to characterize unknown systematics. We demonstrate
that while we do not have sufficient information to correct for unknown
systematics in the data, we can obtain an estimate of their magnitude. We
define a parameter to estimate contamination from unknown systematics using
cross-correlations between different redshift slices and propose discarding
bins in the angular power spectrum that lie outside a certain contamination
tolerance level. We show that this method improves estimates of the bias using
simulated data and further apply it to photometric luminous red galaxies in the
Sloan Digital Sky Survey as a case study.Comment: 24 pages, 6 figures; Expanded discussion of results, added figure 2;
Version to be published in JCA
High-redshift Extremely Red Quasars in X-Rays
Quasars may have played a key role in limiting the stellar mass of massive galaxies. Identifying those quasars in the process of removing star formation fuel from their hosts is an exciting ongoing challenge in extragalactic astronomy. In this paper, we present X-ray observations of 11 extremely red quasars (ERQs) with L bol ~ 1047 erg sâ1 at z = 1.5â3.2 with evidence for high-velocity (v 1000 km sâ1) [O iii] λ5007 outflows. X-rays allow us to directly probe circumnuclear obscuration and to measure the instantaneous accretion luminosity. We detect 10 out of 11 ERQs available in targeted and archival data. Using a combination of X-ray spectral fitting and hardness ratios, we find that all of the ERQs show signs of absorption in the X-rays with inferred column densities of N H â 1023 cmâ2, including four Compton-thick candidates (N H 1024 cmâ2). We stack the X-ray emission of the seven weakly detected sources, measuring an average column density of N H ~ 8 Ă 1023 cmâ2. The absorption-corrected (intrinsic) 2â10 keV X-ray luminosity of the stack is 2.7 Ă 1045 erg sâ1, consistent with X-ray luminosities of type 1 quasars of the same infrared luminosity. Thus, we find that ERQs are a highly obscured, borderline Compton-thick population, and based on optical and infrared data we suggest that these objects are partially hidden by their own equatorial outflows. However, unlike some quasars with known outflows, ERQs do not appear to be intrinsically underluminous in X-rays for their bolometric luminosity. Our observations indicate that low X-rays are not necessary to enable some types of radiatively driven winds
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