73 research outputs found
Spectroscopic Identification of Type 2 Quasars at Z < 1 in SDSS-III/BOSS
The physics and demographics of type 2 quasars remain poorly understood, and
new samples of such objects selected in a variety of ways can give insight into
their physical properties, evolution, and relationship to their host galaxies.
We present a sample of 2758 type 2 quasars at z 1 from the SDSS-III/BOSS
spectroscopic database, selected on the basis of their emission-line
properties. We probe the luminous end of the population by requiring the
rest-frame equivalent width of [OIII] to be > 100 {\AA}. We distinguish our
objects from star-forming galaxies and type 1 quasars using line widths,
standard emission line ratio diagnostic diagrams at z < 0.52 and detection of
[Ne V]{\lambda}3426{\AA} at z > 0.52. The majority of our objects have [OIII]
luminosities in the range 10^8.5-10^10 L and redshifts between 0.4
and 0.65. Our sample includes over 400 type 2 quasars with incorrectly measured
redshifts in the BOSS database; such objects often show kinematic substructure
or outflows in the [OIII] line. The majority of the sample has counterparts in
the WISE survey, with median infrared luminosity {\nu}L{\nu}[12{\mu}m] = 4.2 x
10^44 erg/sec. Only 34 per cent of the newly identified type 2 quasars would be
selected by infrared color cuts designed to identify obscured active nuclei,
highlighting the difficulty of identifying complete samples of type 2 quasars.
We make public the multi-Gaussian decompositions of all [OIII] profiles for the
new sample and for 568 type 2 quasars from SDSS I/II, together with
non-parametric measures of line profile shapes and identify over 600 candidate
double-peaked [OIII] profiles.Comment: 15 pages, 15 figures, 2 tables. Online tables:
http://zakamska.johnshopkins.edu/data.ht
Full forward model of galaxy clustering statistics with simulation lightcones
Novel summary statistics beyond the standard 2-point correlation function
(2PCF) are necessary to capture the full astrophysical and cosmological
information from the small-scale (Mpc) galaxy clustering.
However, the analysis of beyond-2PCF statistics on small scales is challenging
because we lack the appropriate treatment of observational systematics for
arbitrary summary statistics of the galaxy field. In this paper, we develop a
full forward modeling pipeline for any summary statistics using high-fidelity
simulation lightcones that accounts for all observational systematics and is
appropriate for a wide range of summary statistics. We apply our forward model
approach to a fully realistic mock galaxy catalog and demonstrate that we can
recover unbiased constraints on the underlying galaxy--halo connection model
using two separate summary statistics: the standard 2PCF and the novel -th
nearest neighbor (NN) statistics, which are sensitive to correlation
functions of all orders. We expect that applying this forward model approach to
current and upcoming surveys while leveraging a multitude of summary statistics
will become a powerful technique in maximally extracting information from the
non-linear scales.Comment: comments welcom
Precise Cosmological Constraints from BOSS Galaxy Clustering with a Simulation-Based Emulator of the Wavelet Scattering Transform
We perform a reanalysis of the BOSS CMASS DR12 galaxy dataset using a
simulation-based emulator for the Wavelet Scattering Transform (WST)
coefficients. Moving beyond our previous works, which laid the foundation for
the first galaxy clustering application of this estimator, we construct a
neural net-based emulator for the cosmological dependence of the WST
coefficients and the 2-point correlation function multipoles, trained from the
state-of-the-art suite of \textsc{AbacusSummit} simulations combined with a
flexible Halo Occupation Distribution (HOD) galaxy model. In order to confirm
the accuracy of our pipeline, we subject it to a series of thorough internal
and external mock parameter recovery tests, before applying it to reanalyze the
CMASS observations in the redshift range . We find that a joint
WST + 2-point correlation function likelihood analysis allows us to obtain
marginalized 1 errors on the CDM parameters that are tighter
by a factor of , compared to the 2-point correlation function, and by a
factor of compared to the WST-only results. This corresponds to a
competitive , and level of determination for parameters
, , respectively, and also to a
constraint on derived parameters h and , in agreement
with the \textit{Planck} 2018 results. Our results reaffirm the constraining
power of the WST and highlight the exciting prospect of employing higher-order
statistics in order to fully exploit the power of upcoming Stage-IV
spectroscopic observations.Comment: 25 pages, 17 figures, 4 table
2D k-th nearest neighbor statistics: a highly informative probe of galaxy clustering
Beyond standard summary statistics are necessary to summarize the rich
information on non-linear scales in the era of precision galaxy clustering
measurements. For the first time, we introduce the 2D k-th nearest neighbor
(kNN) statistics as a summary statistic for discrete galaxy fields. This is a
direct generalization of the standard 1D kNN by disentangling the projected
galaxy distribution from the redshift-space distortion signature along the
line-of-sight. We further introduce two different flavors of 2D NNs that
trace different aspects of the galaxy field: the standard flavor which
tabulates the distances between galaxies and random query points, and a ''DD''
flavor that tabulates the distances between galaxies and galaxies. We showcase
the 2D kNNs' strong constraining power both through theoretical arguments and
by testing on realistic galaxy mocks. Theoretically, we show that 2D kNNs are
computationally efficient and directly generate other statistics such as the
popular 2-point correlation function, voids probability function, and
counts-in-cell statistics. In a more practical test, we apply the 2D kNN
statistics to simulated galaxy mocks that fold in a large range of
observational realism and recover parameters of the underlying extended halo
occupation distribution (HOD) model that includes velocity bias and galaxy
assembly bias. We find unbiased and significantly tighter constraints on all
aspects of the HOD model with the 2D kNNs, both compared to the standard 1D
kNN, and the classical redshift-space 2-point correlation functions.Comment: Submitted to MNRAS, comments welcom
Robust cosmological inference from non-linear scales with k-th nearest neighbor statistics
We present the methodology for deriving accurate and reliable cosmological
constraints from non-linear scales (<50Mpc/h) with k-th nearest neighbor (kNN)
statistics. We detail our methods for choosing robust minimum scale cuts and
validating galaxy-halo connection models. Using cross-validation, we identify
the galaxy-halo model that ensures both good fits and unbiased predictions
across diverse summary statistics. We demonstrate that we can model kNNs
effectively down to transverse scales of rp ~ 3Mpc/h and achieve precise and
unbiased constraints on the matter density and clustering amplitude, leading to
a 2% constraint on sigma_8. Our simulation-based model pipeline is resilient to
varied model systematics, spanning simulation codes, halo finding, and
cosmology priors. We demonstrate the effectiveness of this approach through an
application to the Beyond-2p mock challenge. We propose further explorations to
test more complex galaxy-halo connection models and tackle potential
observational systematics.Comment: 18 pages, 16 figures, submitted to MNRAS, comments welcom
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