23 research outputs found
Long Period Variables in Local Group Dwarf Galaxies
In this work the results are presented of an extensive search for Long Period Variables stars (LPVs) in a sample of Local Group irregular dwarf galaxies. The methods applied for the detection and the extraction of the variable sources are explained. Extensive completeness simulations were carried out to asses the impact on the resulting catalog caused by the observing pattern and algorithms used.
The resulting catalog of LPVs was together with color-magnitude diagrams used to draw conclusions on the star-formation history in these galaxies
M31 PAndromeda Cepheid sample observed in four HST bands
Using the M31 PAndromeda Cepheid sample and the HST PHAT data we obtain the
largest Cepheid sample in M31 with HST data in four bands. For our analysis we
consider three samples: A very homogeneous sample of Cepheids based on the
PAndromeda data, the mean magnitude corrected PAndromeda sample and a sample
complementing the PAndromeda sample with Cepheids from literature. The latter
results in the largest catalog with 522 fundamental mode (FM) Cepheids and 102
first overtone (FO) Cepheids with F160W and F110W data and 559 FM Cepheids and
111 FO Cepheids with F814W and F475W data. The obtained dispersion of the
Period-Luminosity relations (PLRs) is very small (e.g. 0.138 mag in the F160W
sample I PLR). We find no broken slope in the PLRs when analyzing our entire
sample, but we do identify a subsample of Cepheids that causes the broken
slope. However, this effect only shows when the number of this Cepheid type
makes up a significant fraction of the total sample. We also analyze the sample
selection effect on the Hubble constant.Comment: 32 pages, 19 figures, 9 tables, accepted for publication in ApJ,
electronic data will be available on CD
Photometric Redshifts and Systematic Variations in the SEDs of Luminous Red Galaxies from the SDSS DR7
We describe the construction of a template set of spectral energy
distributions (SEDs) for the estimation of photometric redshifts of luminous
red galaxies (LRGs) with a Bayesian template fitting method. By examining the
color properties of several publicly available SED sets within a redshift range
of 0<z<0.5 and comparing them to SDSS DR7 data, we show that only some of the
investigated SEDs approximately match the colors of the LRG data throughout the
redshift range, however not at the quantitative level required for precise
photometric redshifts. We generate new SEDs by superposing model SEDs of
composite stellar populations with a burst model, allowing both components to
be reddened by dust, in order to match the data in five different redshift
bins. We select a set of SEDs which represents the LRG data in color space
within five redshift bins, thus defining our new SED template set for
photometric redshift estimates. The results we get with the new template set
and our Bayesian template fitting photometric redshift code (PhotoZ) are nearly
unbiased, with a scatter of \sigma(\Delta z)=0.027 (including outliers), and a
fraction of catastrophic outliers (|z_phot-z_spec|/(1+z_spec)>0.15) of 0.12%.
We show that templates that optimally describe the brightest galaxies
(-24.5<M_R<-22.7) indeed vary from z=0.1 to z=0.5, consistent with aging of the
stellar population. Furthermore, we find that templates that optimally describe
galaxies at z<0.1 strongly differ as a function of the absolute magnitude of
the galaxies, indicating an increase in star formation activity for less
luminous galaxies. Our findings based on the photometry of the SDSS LRGs and
our SED template fitting are supported by comparison to the average SDSS LRG
spectra in different luminosity and redshift bins.Comment: 21 pages, 25 figures, accepted for publication in the Astrophysical
Journal (ApJ
Implementation of PhotoZ under Astro-WISE - A photometric redshift code for large datasets
We describe the implementation of the PhotoZ code in the framework of the
Astro-WISE package and as part of the Photometric Classification Server of the
PanSTARRS pipeline. Both systems allow the automatic measurement of photometric
redshifts for the millions of objects being observed in the PanSTARRS project
or expected to be observed by future surveys like KIDS, DES or EUCLID.Comment: Accepted for publication in topical issue of Experimental Astronomy
on Astro-WISE information system, references update
Properties of M31. II: A Cepheid disk sample derived from the first year of PS1 PAndromeda data
We present a sample of Cepheid variable stars towards M31 based on the first
year of regular M31 observations of the PS1 survey in the r_P1 and i_P1
filters. We describe the selection procedure for Cepheid variable stars from
the overall variable source sample and develop an automatic classification
scheme using Fourier decomposition and the location of the instability strip.
We find 1440 fundamental mode (classical \delta) Cep stars, 126 Cepheids in the
first overtone mode, and 147 belonging to the Population II types. 296 Cepheids
could not be assigned to one of these classes and 354 Cepheids were found in
other surveys. These 2009 Cepheids constitute the largest Cepheid sample in M31
known so far and the full catalog is presented in this paper. We briefly
describe the properties of our sample in its spatial distribution throughout
the M31 galaxy, in its age properties, and we derive an apparent
period-luminosity relation (PLR) in our two bands. The Population I Cepheids
nicely follow the dust pattern of the M31 disk, whereas the 147 Type II
Cepheids are distributed throughout the halo of M31. We outline the time
evolution of the star formation in the major ring found previously and find an
age gradient. A comparison of our PLR to previous results indicates a curvature
term in the PLR
Cepheids in M31: The PAndromeda Cepheid Sample
We present the largest Cepheid sample in M31 based on the complete Pan-STARRS1 survey of Andromeda (PAndromeda) in the r P1, i P1, and g P1 bands. We find 2686 Cepheids with 1662 fundamental-mode Cepheids, 307 first-overtone Cepheids, 278 type II Cepheids, and 439 Cepheids with undetermined Cepheid type. Using the method developed by Kodric et al., we identify Cepheids by using a three-dimensional parameter space of Fourier parameters of the Cepheid light curves combined with a color cut and other selection criteria. This is an unbiased approach to identify Cepheids and results in a homogeneous Cepheid sample. The period–luminosity relations obtained for our sample have smaller dispersions than in our previous work. We find a broken slope that we previously observed with HST data in Kodric et al., albeit with a lower significance
HETDEX Public Source Catalog 1 -- Stacking 50K Lyman Alpha Emitters
We describe the ensemble properties of the Lyman Alpha
Emitters (LAEs) found in the HETDEX survey's first public data release, HETDEX
Public Source Catalog 1 (Mentuch Cooper et al. 2023). Stacking the
low-resolution ( 800) spectra greatly increases the signal-to-noise
ratio, revealing spectral features otherwise hidden by noise, and we show that
the stacked spectrum is representative of an average member of the set. The
flux limited, Ly signal-to-noise ratio restricted stack of 50K HETDEX
LAEs shows the ensemble biweight ``average" LAE to be a blue (UV
continuum slope and E(B-V) ), moderately bright
(M) star forming galaxy with strong Ly
emission (log 42.8 and (Ly)
114\AA), and potentially significant leakage of ionizing radiation. The
restframe UV light is dominated by a young, metal poor stellar population with
an average age 5-15 Myr and metallicity of 0.2-0.3 Z.Comment: 17 pages, 11 figures, 2 data files (ApJ Accepted