13 research outputs found
Tidal interactions at the edge of the Local Group: New evidence for tidal features in the Antlia Dwarf Galaxy
Using deep B band imaging down to mu_{B} = 26 mag arcsec^{-2}, we present
evidence for tidal tails in the Antlia Dwarf galaxy, one of the most distant
members of the Local Group. This elongation is in the direction of Antlia's
nearest neighbor, the Magellanic-type NGC 3109. The tail is offset by less than
10 degrees from a vector linking the centers of the two galaxies, indicative of
interactions between the pair. Combined with the warped disc previously
identified in NGC 3109, Antlia and NGC 3109 must be at a small separation for
tidal features to be present in Antlia. We calculate that Antlia cannot be
completely disrupted by NGC 3109 in a single interaction unless its orbit
pericenter is less than 6 kpc, however multiple interactions could
significantly alter its morphology. Therefore despite being located right at
the edge of the Local Group, environmental effects are playing an important
role in Antlia's evolution.Comment: 8 pages, 4 figures, accepted for publication in ApJ
A Critical Assessment of Stellar Mass Measurement Methods
In this paper we perform a comprehensive study of the main sources of random
and systematic errors in stellar mass measurement for galaxies using their
Spectral Energy Distributions (SEDs). We use mock galaxy catalogs with
simulated multi-waveband photometry (from U-band to mid-infrared) and known
redshift, stellar mass, age and extinction for individual galaxies. Given
different parameters affecting stellar mass measurement (photometric S/N
ratios, SED fitting errors, systematic effects, the inherent degeneracies and
correlated errors), we formulated different simulated galaxy catalogs to
quantify these effects individually. We studied the sensitivity of stellar mass
estimates to the codes/methods used, population synthesis models, star
formation histories, nebular emission line contributions, photometric
uncertainties, extinction and age. For each simulated galaxy, the difference
between the input stellar masses and those estimated using different simulation
catalogs, , was calculated and used to identify the most
fundamental parameters affecting stellar masses. We measured different
components of the error budget, with the results listed as follows: (1). no
significant bias was found among different codes/methods, with all having
comparable scatter; (2). A source of error is found to be due to photometric
uncertainties and low resolution in age and extinction grids; (3). The median
of stellar masses among different methods provides a stable measure of the mass
associated with any given galaxy; (4). The deviations in stellar mass strongly
correlate with those in age, with a weaker correlation with extinction; (5).
the scatter in the stellar masses due to free parameters are quantified, with
the sensitivity of the stellar mass to both the population synthesis codes and
inclusion of nebular emission lines studied.Comment: 33 pages, 20 Figures, Accepted for publication in Astrophysical
Journa
CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey - The Hubble Space Telescope Observations, Imaging Data Products and Mosaics
This paper describes the Hubble Space Telescope imaging data products and
data reduction procedures for the Cosmic Assembly Near-IR Deep Extragalactic
Legacy Survey (CANDELS). This survey is designed to document the evolution of
galaxies and black holes at , and to study Type Ia SNe beyond
. Five premier multi-wavelength sky regions are selected, each with
extensive multiwavelength observations. The primary CANDELS data consist of
imaging obtained in the Wide Field Camera 3 / infrared channel (WFC3/IR) and
UVIS channel, along with the Advanced Camera for Surveys (ACS). The
CANDELS/Deep survey covers \sim125 square arcminutes within GOODS-N and
GOODS-S, while the remainder consists of the CANDELS/Wide survey, achieving a
total of \sim800 square arcminutes across GOODS and three additional fields
(EGS, COSMOS, and UDS). We summarize the observational aspects of the survey as
motivated by the scientific goals and present a detailed description of the
data reduction procedures and products from the survey. Our data reduction
methods utilize the most up to date calibration files and image combination
procedures. We have paid special attention to correcting a range of
instrumental effects, including CTE degradation for ACS, removal of electronic
bias-striping present in ACS data after SM4, and persistence effects and other
artifacts in WFC3/IR. For each field, we release mosaics for individual epochs
and eventual mosaics containing data from all epochs combined, to facilitate
photometric variability studies and the deepest possible photometry. A more
detailed overview of the science goals and observational design of the survey
are presented in a companion paper.Comment: 39 pages, 25 figure
Demographics of Star-forming Galaxies since z ⌠2.5. I. The <i>UVJ </i>Diagram in CANDELS
This is the first in a series of papers examining the demographics of
star-forming galaxies at in CANDELS. We study 9,100 galaxies from
GOODS-S and UDS having published values of redshifts, masses, star-formation
rates (SFRs), and dust attenuation () derived from UV-optical SED fitting.
In agreement with previous works, we find that the colors of a galaxy are
closely correlated with its specific star-formation rate (SSFR) and . We
define rotated coordinate axes, termed and
, that are parallel and perpendicular to the star-forming
sequence and derive a quantitative calibration that predicts SSFR from
with an accuracy of ~0.2 dex. SFRs from UV-optical fitting and
from UV+IR values based on Spitzer/MIPS 24 agree well overall,
but systematic differences of order 0.2 dex exist at high and low redshifts. A
novel plotting scheme conveys the evolution of multiple galaxy properties
simultaneously, and dust growth, as well as star-formation decline and
quenching, exhibit "mass-accelerated evolution" ("downsizing"). A population of
transition galaxies below the star-forming main sequence is identified. These
objects are located between star-forming and quiescent galaxies in space
and have lower and smaller radii than galaxies on the main sequence.
Their properties are consistent with their being in transit between the two
regions. The relative numbers of quenched, transition, and star-forming
galaxies are given as a function of mass and redshift.Comment: 36 pages, 26 figures, ApJ accepte
SINFONI/VLT 3D spectroscopy of massive galaxies: evidence of rotational support at z similar to 1.4
International audienceThere is cumulative evidence showing that, for the most massive galaxies, the fraction of disc-like objects compared to those with spheroidal properties increases with redshift. However, this evolution is thus far based on the surface brightness study of these objects. To explore the consistency of this scenario, it is necessary to measure the dynamical status of these galaxies. With this aim, we have obtained seeing-limited near-infrared integral-field spectra in the H-band for 10 massive galaxies (M-* \textgreater=10(11) h(70)(-2)M(circle dot)) at z similar to 1.4 with SINFONI at the VLT. Our sample is selected by their stellar mass and EW[O ii] \textgreater 15 A, to secure their kinematic measurements, but without accounting for any morphological or flux criteria a priori. Through this 3D kinematic spectroscopy analysis, we find that half (i.e. 50 +/- 7 per cent) of our galaxies are compatible with being rotationally supported discs, in agreement with previous morphological expectations. This is a factor of approximately 2 higher than what is observed in the present Universe for objects of the same stellar mass. Strikingly, the majority of our sample of massive galaxies show extended and fairly high rotational velocity maps, implying that massive galaxies acquire rapidly rotational support and hence gravitational equilibrium. Our sample also show evidence for ongoing interactions and mergers. Summarizing, massive galaxies at high-z show a significant diversity and must have continued evolution beyond the fading of stellar populations, to become their present-day counterparts
A Critical Assessment of Stellar Mass Measurement Methods
This is the second paper in a series aimed at investigating the main sources of uncertainty in measuring the observable parameters in galaxies from their spectral energy distributions (SEDs). In the first paper we presented a detailed account of the photometric redshift measurements and an error analysis of this process. In this paper we perform a comprehensive study of the main sources of random and systematic error in stellar mass estimates for galaxies, and their relative contributions to the associated error budget. Since there is no prior knowledge of the stellar mass of galaxies (unlike their photometric redshifts), we use mock galaxy catalogs with simulated multi-waveband photometry and known redshift, stellar mass, age and extinction for individual galaxies. The multi-waveband photometry for the simulated galaxies were generated in 13 filters spanning from U-band to mid-infrared wavelengths. Given different parameters affecting stellar mass measurement (photometric signal-to-noise ratios (S/N), SED fitting errors and systematic effects), the inherent degeneracies and correlated errors, we formulated different simulated galaxy catalogs to quantify these effects individually. For comparison, we also generated catalogs based on observed photometric data of real galaxies in the Great Observatories Origins Deep Survey-South field, spanning the same passbands. The simulated and observed catalogs were provided to a number of teams within the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey collaboration to estimate the stellar masses for individual galaxies. A total of 11 teams participated, with different combinations of stellar mass measurement codes/methods, population synthesis models, star formation histories, extinction and age. For each simulated galaxy, the differences between the input stellar masses, Minput, and those estimated by each team, Mest, is defined as , and used to identify the most fundamental parameters affecting stellar mass estimate in galaxies, with the following results. (1) No significant bias in Î log(M) was found among different codes, with all having comparable scatter ( dex). The estimated stellar mass values are seriously affected by low photometric S/N, with the rms scatter increasing for galaxies with mag; (2) A source of error contributing to the scatter in Î log(M) is found to be due to photometric uncertainties (0.136 dex) and low resolution in age and extinction grids when generating the SED templates; (3) The median of stellar masses among different methods provides a stable measure of the mass associated with any given galaxy ( dex); (4) The Î log(M) values are strongly correlated with deviations in age (defined as the difference between the estimated and expected values), with a weaker correlation with extinction; (5) The rms scatter in the estimated stellar masses due to free parameters (after fixing redshifts and initial mass function) are quantified and found to be dex; (6) Using the observed data, we studied the sensitivity of stellar masses to both the population synthesis codes and inclusion of nebular emission lines and found them to affect the stellar mass by 0.2 and 0.3 dex respectively
Demographics of Star-forming Galaxies since z ⌠2.5. I. The <i>UVJ </i>Diagram in CANDELS
This is the first in a series of papers examining the demographics of star-forming (SF) galaxies at 0.2 < z < 2.5 in CANDELS. We study 9100 galaxies from GOODS-S and UDS, having published values of redshifts, masses, star formation rates (SFRs), and dust attenuation (A V) derived from UV-optical spectral energy distribution fitting. In agreement with previous works, we find that the UVJ colors of a galaxy are closely correlated with its specific star formation rate (SSFR) and A V. We define rotated UVJ coordinate axes, termed S SED and C SED, that are parallel and perpendicular to the SF sequence and derive a quantitative calibration that predicts SSFR from C SED with an accuracy of âŒ0.2 dex. SFRs from UV-optical fitting and from UV+IR values based on Spitzer/MIPS 24 ÎŒm agree well overall, but systematic differences of order 0.2 dex exist at high and low redshifts. A novel plotting scheme conveys the evolution of multiple galaxy properties simultaneously, and dust growth, as well as star formation decline and quenching, exhibit "mass-accelerated evolution" ("downsizing"). A population of transition galaxies below the SF main sequence is identified. These objects are located between SF and quiescent galaxies in UVJ space, and have lower A V and smaller radii than galaxies on the main sequence. Their properties are consistent with their being in transit between the two regions. The relative numbers of quenched, transition, and SF galaxies are given as a function of mass and redshift. </p
A Critical Assessment Of Photometric Redshift Methods: A CANDELS Investigation
We present results from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) photometric redshift methods investigation. In this investigation, the results from 11 participants, each using a different combination of photometric redshift code, template spectral energy distributions (SEDs), and priors, are used to examine the properties of photometric redshifts applied to deep fields with broadband multi-wavelength coverage. The photometry used includes U-band through mid-infrared filters and was derived using the TFIT method. Comparing the results, we find that there is no particular code or set of template SEDs that results in significantly better photometric redshifts compared to others. However, we find that codes producing the lowest scatter and outlier fraction utilize a training sample to optimize photometric redshifts by adding zero-point offsets, template adjusting, or adding extra smoothing errors. These results therefore stress the importance of the training procedure. We find a strong dependence of the photometric redshift accuracy on the signal-to-noise ratio of the photometry. On the other hand, we find a weak dependence of the photometric redshift scatter with redshift and galaxy color. We find that most photometric redshift codes quote redshift errors (e.g., 68% confidence intervals) that are too small compared to that expected from the spectroscopic control sample. We find that all codes show a statistically significant bias in the photometric redshifts. However, the bias is in all cases smaller than the scatter; the latter therefore dominates the errors. Finally, we find that combining results from multiple codes significantly decreases the photometric redshift scatter and outlier fraction. We discuss different ways of combining data to produce accurate photometric redshifts and error estimates.NASA NAS 5-26555, GO-9352, GO-9425, GO-9583, GO-9728, GO-10189, GO-10339, GO-10340, GO-11359, GO-12060, GO-12061Astronom