89 research outputs found
Étude du taux de formation d'étoiles dans les galaxies du Gemini Deep Deep Survey
Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal
Fast and efficient identification of anomalous galaxy spectra with neural density estimation
Current large-scale astrophysical experiments produce unprecedented amounts
of rich and diverse data. This creates a growing need for fast and flexible
automated data inspection methods. Deep learning algorithms can capture and
pick up subtle variations in rich data sets and are fast to apply once trained.
Here, we study the applicability of an unsupervised and probabilistic deep
learning framework, the Probabilistic Autoencoder (PAE), to the detection of
peculiar objects in galaxy spectra from the SDSS survey. Different to
supervised algorithms, this algorithm is not trained to detect a specific
feature or type of anomaly, instead it learns the complex and diverse
distribution of galaxy spectra from training data and identifies outliers with
respect to the learned distribution. We find that the algorithm assigns
consistently lower probabilities (higher anomaly score) to spectra that exhibit
unusual features. For example, the majority of outliers among quiescent
galaxies are E+A galaxies, whose spectra combine features from old and young
stellar population. Other identified outliers include LINERs, supernovae and
overlapping objects. Conditional modeling further allows us to incorporate
additional information. Namely, we evaluate the probability of an object being
anomalous given a certain spectral class, but other information such as metrics
of data quality or estimated redshift could be incorporated as well. We make
our code publicly available at https://github.com/VMBoehm/Spectra_PAEComment: 16 pages, 14 figures, MNRAS revised manuscript after addressing the
report from the referee. Our first paper is available at arXiv:2211.11783 .
Our code is publicly available at https://github.com/VMBoehm/Spectra_PA
IROCKS: Spatially Resolved Kinematics of z ~ 1 Star-forming Galaxies
We present results from the Intermediate Redshift OSIRIS Chemo-Kinematic Survey (IROCKS) for sixteen z ~ 1 and one z ~ 1.4 star-forming galaxies. All galaxies were observed with OSIRIS with the laser guide star adaptive optics system at Keck Observatory. We use rest-frame nebular Hα emission lines to trace morphologies and kinematics of ionized gas in star-forming galaxies on sub-kiloparsec physical scales. We observe elevated velocity dispersions (σ ≳ 50 km s^(−1)) seen in z > 1.5 galaxies persist at z ~ 1 in the integrated galaxies. Using an inclined disk model and the ratio of v/σ, we find that 1/3 of the z ~ 1 sample are disk candidates while the other 2/3 of the sample are dominated by merger-like and irregular sources. We find that including extra attenuation toward H ii regions derived from stellar population synthesis modeling brings star formation rates (SFRs) using Hα and stellar population fit into a better agreement. We explore the properties of the compact Hα sub-component, or "clump," at z ~ 1 and find that they follow a similar size–luminosity relation as local H ii regions but are scaled-up by an order of magnitude with higher luminosities and sizes. Comparing the z ~ 1 clumps to other high-redshift clump studies, we determine that the clump SFR surface density evolves as a function of redshift. This suggests clump formation is directly related to the gas fraction in these systems and may support disk fragmentation as their formation mechanism since gas fraction scales with redshift
Evolved Galaxies at z > 1.5 from the Gemini Deep Deep Survey: The Formation Epoch of Massive Stellar Systems
We present spectroscopic evidence from the Gemini Deep Deep Survey (GDDS) for
a significant population of color-selected red galaxies at 1.3 < z < 2.2 whose
integrated light is dominated by evolved stars. Unlike radio-selected objects,
the z > 1.5 old galaxies have a sky density > 0.1 per sq. arcmin. Conservative
age estimates for 20 galaxies with z > 1.3; = 1.49, give a median age of
1.2 Gyr and = 2.4. One quarter of the galaxies have inferred z_f > 4.
Models restricted to abundances less than or equal to solar give median ages
and z_f of 2.3 Gyr and 3.3, respectively. These galaxies are among the most
massive and contribute approximately 50% of the stellar mass density at 1 < z <
2. The derived ages and most probable star formation histories suggest a high
star-formation-rate (300-500 solar masses per year) phase in the progenitor
population. We argue that most of the red galaxies are not descendants of the
typical z=3 Lyman break galaxies. Galaxies associated with luminous sub-mm
sources have the requisite star formation rates to be the progenitor
population. Our results point toward early and rapid formation for a
significant fraction of present day massive galaxies.Comment: 12 pages, 2 figures, 1 table, Accepted for publication, ApJ Letter
Cosmic Star Formation History and its Dependence on Galaxy Stellar Mass
We examine the cosmic star formation rate (SFR) and its dependence on galaxy
stellar mass over the redshift range 0.8 < z < 2 using data from the Gemini
Deep Deep Survey (GDDS). The SFR in the most massive galaxies (M > 10^{10.8}
M_sun) was six times higher at z = 2 than it is today. It drops steeply from z
= 2, reaching the present day value at z ~ 1. In contrast, the SFR density of
intermediate mass galaxies (10^{10.2} < M < 10^{10.8} M_sun) declines more
slowly and may peak or plateau at z ~ 1.5. We use the characteristic growth
time t_SFR = rho_M / rho_SFR to provide evidence of an associated transition in
massive galaxies from a burst to a quiescent star formation mode at z ~ 2.
Intermediate mass systems transit from burst to quiescent mode at z ~ 1, while
the lowest mass objects undergo bursts throughout our redshift range. Our
results show unambiguously that the formation era for galaxies was extended and
proceeded from high to low mass systems. The most massive galaxies formed most
of their stars in the first ~3 Gyr of cosmic history. Intermediate mass objects
continued to form their dominant stellar mass for an additional ~2 Gyr, while
the lowest mass systems have been forming over the whole cosmic epoch spanned
by the GDDS. This view of galaxy formation clearly supports `downsizing' in the
SFR where the most massive galaxies form first and galaxy formation proceeds
from larger to smaller mass scales.Comment: Accepted for publication in ApJ
Probing the Physics of Narrow Line Regions in Active Galaxies II: The Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7)
Here we describe the \emph{Siding Spring Southern Seyfert Spectroscopic
Snapshot Survey} (S7) and present results on 64 galaxies drawn from the first
data release. The S7 uses the Wide Field Spectrograph (WiFeS) mounted on the
ANU 2.3m telescope located at the Siding Spring Observatory to deliver an
integral field of ~ arcsec at a spectral resolution of in
the red (nm), and in the blue (nm). {From these data
cubes we have extracted the Narrow Line Region (NLR) spectra from a 4 arc sec
aperture centred on the nucleus. We also determine the H and
[OIII]~5007 fluxes in the narrow lines, the nuclear reddening, the
reddening-corrected relative intensities of the observed emission lines, and
the H and \lOIII\ luminosities {determined from spectra for which the
stellar continuum has been removed.} We present a set of images of the galaxies
in [OIII]~5007, [NII]~6584 and H which serve to
delineate the spatial extent of the extended narrow line region (ENLR) and {\bf
also to} reveal the structure and morphology of the surrounding \HII\ regions.
Finally, we provide a preliminary discussion of those Seyfert~1 and Seyfert~2
galaxies which display coronal emission lines in order to explore the origin of
these lines.Comment: Accepted for publication 9 Jan 2015, Astrophysical Journal
Supplements. 49pages, 8 figure
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