223 research outputs found
Accurate mass and velocity functions of dark matter halos
-body cosmological simulations are an essential tool to understand the
observed distribution of galaxies. We use the MultiDark simulation suite, run
with the Planck cosmological parameters, to revisit the mass and velocity
functions. At redshift , the simulations cover four orders of magnitude in
halo mass from with 8,783,874 distinct halos and 532,533
subhalos. The total volume used is 515 Gpc, more than 8 times larger
than in previous studies. We measure and model the halo mass function, its
covariance matrix w.r.t halo mass and the large scale halo bias. With the
formalism of the excursion-set mass function, we explicit the tight
interconnection between the covariance matrix, bias and halo mass function. We
obtain a very accurate ( level) model of the distinct halo mass function.
We also model the subhalo mass function and its relation to the distinct halo
mass function. The set of models obtained provides a complete and precise
framework for the description of halos in the concordance Planck cosmology.
Finally, we provide precise analytical fits of the maximum velocity
function up to redshift to push for the development of halo occupation
distribution using . The data and the analysis code are made publicly
available in the \textit{Skies and Universes} database.Comment: Corresponding data is available at the Skies and Universes data base:
http://projects.ift.uam-csic.es/skies-universe
A study of 1000 galaxies with unusually young and massive stars in the SDSS: a search for hidden black holes
We select 1076 galaxies with extinction-corrected Halpha equivalent widths
too large to be explained with a Kroupa (2001) IMF, and compare these with a
control sample of galaxies that is matched in stellar mass, redshift and 4000
AA break strength, but with normal Halpha equivalent widths. Our goal is to
study how processes such as black hole growth and energetic feedback processes
from massive stars differ between galaxies with extreme central Halpha emission
and galaxies with normal young central stellar populations. The stellar mass
distribution of Halpha excess galaxies is peaked at 3 \times 10^10 Msun and
almost all fall well within the star-forming locus in the [OIII]/Hbeta versus
[NII]/Halpha BPT disgram. Halpha excess galaxies are twice as likely to exhibit
Halpha line asymmetries and 1.55 times more likely to be detected at 1 GHz in
the VLA FIRST survey compared to control sample galaxies. The radio luminosity
per unit stellar mass decreases with the stellar age of the system. Using
stacked spectra, we demonstrate that [NeV] emission is not present in the very
youngest of the radio-quiet Halpha excess galaxies with detectable Wolf-Rayet
features, suggesting that black hole growth has not yet commenced in such
systems. [NeV] emission is detected in Halpha excess galaxies with radio
detections and the strength of the line correlates with the radio luminosity.
This is the clearest indication for a possible population of black holes that
may be forming in a subset of the Halpha excess population.Comment: 17 pages, 22 figures, accepted in MNRA
Measuring galaxy [OII] emission line doublet with future ground-based wide-field spectroscopic surveys
The next generation of wide-field spectroscopic redshift surveys will map the
large-scale galaxy distribution in the redshift range 0.7< z<2 to measure
baryonic acoustic oscillations (BAO). The primary optical signature used in
this redshift range comes from the [OII] emission line doublet, which provides
a unique redshift identification that can minimize confusion with other single
emission lines. To derive the required spectrograph resolution for these
redshift surveys, we simulate observations of the [OII] (3727,3729) doublet for
various instrument resolutions, and line velocities. We foresee two strategies
about the choice of the resolution for future spectrographs for BAO surveys.
For bright [OII] emitter surveys ([OII] flux ~30.10^{-17} erg /cm2/s like
SDSS-IV/eBOSS), a resolution of R~3300 allows the separation of 90 percent of
the doublets. The impact of the sky lines on the completeness in redshift is
less than 6 percent. For faint [OII] emitter surveys ([OII] flux ~10.10^{-17}
erg /cm2/s like DESi), the detection improves continuously with resolution, so
we recommend the highest possible resolution, the limit being given by the
number of pixels (4k by 4k) on the detector and the number of spectroscopic
channels (2 or 3).Comment: 5 pages, 1 figur
Multi-tracer extension of the halo model:probing quenching and conformity in eBOSS
We develop a new Multi-Tracer Halo Occupation Distribution (\texttt{MTHOD})
framework for the galaxy distribution and apply it to the extended Baryon
Oscillation Spectroscopic Survey (eBOSS) final data between . We
obtain a best fit \mthod\, for each tracer and describe the host halo
properties of these galaxies. The mean halo masses for LRGs, ELGs and QSOs are
found to be 1.9 \times 10^{13} \msolaroh, 1.1 \times 10^{12} \msolaroh and
5 \times 10^{12} \msolaroh respectively in the eBOSS data. We use the
\texttt{MTHOD} framework to create mock galaxy catalogues and predict auto- and
cross-correlation functions for all the tracers. Comparing these results with
data, we investigate galactic conformity, the phenomenon whereby the properties
of neighbouring galaxies are mutually correlated in a manner that is not
captured by the basic halo model. We detect \textsl{1-halo} conformity at more
than 3 statistical significance, while obtaining upper limit on
\textsl{2-halo} conformity. We also look at the environmental dependence of the
galaxy quenching efficiency and find that halo mass driven quenching
successfully explains the behaviour in high density regions, but it fails to
describe the quenching efficiency in low density regions. In particular, we
show that the quenching efficiency in low density filaments is higher in the
observed data, as compared to the prediction of the \mthod\ with halo mass
driven quenching. The mock galaxy catalogue constructed in this paper is
publicly available on https://www.roe.ac.uk/~salam/MTHOD/ .Comment: 17 pages, 12 figures, the software and mock catalogue should be made
available through: https://www.roe.ac.uk/~salam/MTHOD/ , Accepted for
publication in MNRA
Probing AGN Inner Structure with X-ray Obscured Type 1 AGN
Using the X-ray-selected active galactic nuclei (AGN) from the XMM-XXL north
survey and the SDSS Baryon Oscillation Spectroscopic Survey (BOSS)
spectroscopic follow-up of them, we compare the properties of X-ray unobscured
and obscured broad-line AGN (BLAGN1 and BLAGN2; below and above
cm), including their X-ray luminosity , black hole
mass, Eddington ratio , optical continuum and line
features. We find that BLAGN2 have systematically larger broad line widths and
hence apparently higher (lower) ()
than BLAGN1. We also find that the X-ray obscuration in BLAGN tends to coincide
with optical dust extinction, which is optically thinner than that in
narrow-line AGN (NLAGN) and likely partial-covering to the broad line region.
All the results can be explained in the framework of a multi-component, clumpy
torus model by interpreting BLAGN2 as an intermediate type between BLAGN1 and
NLAGN in terms of an intermediate inclination angle.Comment: 21 pages, 12 figures, published in MNRA
The Mass-Concentration Relation and the Stellar-to-Halo Mass Ratio in the CFHT Stripe 82 Survey
We present a new measurement of the mass-concentration relation and the
stellar-to-halo mass ratio over the halo mass range to
. To achieve this, we use weak lensing measurements
from the CFHT Stripe 82 Survey (CS82), combined with the central galaxies from
the redMaPPer cluster catalogue and the LOWZ/CMASS galaxy sample of the Sloan
Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey Tenth Data
Release. The stacked lensing signals around these samples are modelled as a sum
of contributions from the central galaxy, its dark matter halo, and the
neighboring halos, as well as a term for possible centering errors. We measure
the mass-concentration relation: with
for and for . These amplitudes and slopes are completely
consistent with predictions from recent simulations. We also measure the
stellar-to-halo mass ratio for our samples, and find results consistent with
previous measurements from lensing and other techniques.Comment: 10 pages, 3 figures, 3 table
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
Quasars at intermediate redshift are not special; but they are often satellites
Understanding the links between the activity of supermassive black holes
(SMBH) at the centres of galaxies and their host dark matter haloes is a key
question in modern astrophysics. The final data release of the SDSS-IV eBOSS
provides the largest contemporary spectroscopic sample of galaxies and QSOs.
Using this sample and covering the redshift interval , we have
measured the clustering properties of the eBOSS QSOs, Emission Line Galaxies
(ELGs) and Luminous Red Galaxies (LRGs). We have also measured the fraction of
QSOs as a function of the overdensity defined by the galaxy population. Using
these measurements, we investigate how QSOs populate and sample the galaxy
population, and how the host dark-matter haloes of QSOs sample the underlying
halo distribution. We find that the probability of a galaxy hosting a QSO is
independent of the host dark matter halo mass of the galaxy. We also find that
about 60\% of eBOSS QSOs are hosted by LRGs and about 20-40\% of QSOs are
hosted by satellite galaxies. We find a slight preference for QSOs to populate
satellite galaxies over central galaxies. This is connected to the host halo
mass distribution of different types of galaxies. Based on our analysis, QSOs
should be hosted by a very broad distribution of haloes, and their occurrence
should be modulated only by the efficiency of galaxy formation processes.Comment: 15 pages, 6 Figures, Data and code from this analysis is available at
https://www.roe.ac.uk/~salam/GQOD/ , submitted to MNRAS, comments and
suggestions are welcom
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