43 research outputs found
Missing GRB host galaxies in deep mid-infrared observations: implications on the use of GRBs as star formation tracers
We report on the first mid-infrared observations of 16 GRB host galaxies performed with the Spitzer Space Telescope, and investigate the presence of evolved stellar populations and dust-enshrouded star-forming activity associated with GRBs. Only a very small fraction of our sample is detected by Spitzer, which is not consistent with recent works suggesting the presence of a GRB host population dominated by massive and strongly-starbursting galaxies (SFR >~ 100M[sun]yr^–1). Should the GRB hosts be representative of star-forming galaxies at high redshift, models of galaxy evolution indicate that >~ 50% of GRB hosts would be easily detected at the depth of our mid-infrared observations. Unless our sample suffers from a strong observational bias which remains to be understood, we infer in this context that the GRBs identified with the current techniques can not be directly used as unbiased probes of the global and integrated star formation history of the Universe
The [Ne III]/[Ne II] line ratio in NGC 253
We present results of the mapping of the nucleus of the starburst galaxy NGC 253 and its immediate surroundings using the Infrared Spectrograph on board the Spitzer Space Telescope. The map is centered on the nucleus of the galaxy and spans the inner 800 Ă— 688 pc^2. We perform a brief investigation of the implications of these measurement on the properties of the star formation in this region using theories developed to explain the deficiency of massive stars in starbursts
The BHK Color Diagram: a New Tool to Study Young Stellar Populations
A new method to derive age differences between the various super star
clusters observed in starburst galaxies using the two color diagram (B-H) vs
(H-K) is presented. This method offers a quick and easy way to differentiate
very young and intermediate age stellar populations even if data on extinction
are unavailable. In this case, discrimination of regions younger and older than
4 Myr is feasible. With the availability of data on extinction, the time
resolution can be improved significantly. The application of the method to the
starbursting system Arp 299 is presented. The validity of the method is
confirmed by comparing the equivalent width of the H-alpha line with the
chronological map of the northern part of NGC 3690.Comment: 32 pages, 7 figures, 1 table, AJ accepte
Probing the cosmic star formation using long Gamma-Ray Bursts: New constraints from the Spitzer Space Telescope
We report on IRAC-4.5mic, IRAC-8.0mic and MIPS-24mic deep observations of 16
Gamma-Ray Burst (GRBs) host galaxies performed with the Spitzer Space
Telescope, and we investigate in the thermal infrared the presence of evolved
stellar populations and dust-enshrouded star-forming activity associated with
these objects. Our sample is derived from GRBs that were identified with
sub-arcsec localization between 1997 and 2001, and only a very small fraction
(~20%) of the targeted sources is detected down to f_4.5mic ~3.5microJy and
f_24mic ~85microJy (3sigma). This likely argues against a population dominated
by massive and strongly-starbursting (i.e., SFR > ~100 Msol/yr) galaxies as it
has been recently suggested from submillimeter/radio and optical studies of
similarly-selected GRB hosts. Furthermore we find evidence that some GRBs do
not occur in the most infrared-luminous regions -- hence the most actively
star-forming environments -- of their host galaxies. Should the GRB hosts be
representative of all star-forming galaxies at high redshift, models of
infrared galaxy evolution indicate that > ~50% of GRB hosts should have f_24mic
> ~100microJy. Unless the identification of GRBs prior to 2001 was prone to
strong selection effects biasing our sample against dusty galaxies, we infer in
this context that the GRBs identified with the current techniques can not be
directly used as unbiased probes of the global and integrated star formation
history of the Universe.Comment: ApJ in press, 23 pages, 8 figures (scheduled for the ApJ 10 May 2006,
v642 2 issue). Full resolution available at
http://perceval.as.arizona.edu/~elefloch/Publis/ms_grb_spitzer.pd
Starburst99: Synthesis Models for Galaxies with Active Star Formation
Starburst99 is a comprehensive set of model predictions for
spectrophotometric and related properties of galaxies with active star
formation. The models are an improved and extended version of the data set
previously published by Leitherer & Heckman (1995). We have upgraded our code
by implementing the latest set of stellar evolution models of the Geneva group
and the model atmosphere grid compiled by Lejeune et al. (1997). Several
predictions which were not included in the previous publication are shown here
for the first time. The models are presented in a homogeneous way for five
metallicities between Z = 0.040 and 0.001 and three choices of the initial mass
function. The age coverage is 10^6 to 10^9 yr. We also show the spectral energy
distributions which are used to compute colors and other quantities. The full
data set is available for retrieval at
http://www.stsci.edu/science/starburst99/. This website allows users to run
specific models with non-standard parameters as well. We also make the source
code available to the community.Comment: 32 pages, LaTeX. All the Figures and the summary Table are located at
http://www.stsci.edu/science/starburst99/, ApJ accepte
The Maunakea Spectroscopic Explorer Book 2018
(Abridged) This is the Maunakea Spectroscopic Explorer 2018 book. It is
intended as a concise reference guide to all aspects of the scientific and
technical design of MSE, for the international astronomy and engineering
communities, and related agencies. The current version is a status report of
MSE's science goals and their practical implementation, following the System
Conceptual Design Review, held in January 2018. MSE is a planned 10-m class,
wide-field, optical and near-infrared facility, designed to enable
transformative science, while filling a critical missing gap in the emerging
international network of large-scale astronomical facilities. MSE is completely
dedicated to multi-object spectroscopy of samples of between thousands and
millions of astrophysical objects. It will lead the world in this arena, due to
its unique design capabilities: it will boast a large (11.25 m) aperture and
wide (1.52 sq. degree) field of view; it will have the capabilities to observe
at a wide range of spectral resolutions, from R2500 to R40,000, with massive
multiplexing (4332 spectra per exposure, with all spectral resolutions
available at all times), and an on-target observing efficiency of more than
80%. MSE will unveil the composition and dynamics of the faint Universe and is
designed to excel at precision studies of faint astrophysical phenomena. It
will also provide critical follow-up for multi-wavelength imaging surveys, such
as those of the Large Synoptic Survey Telescope, Gaia, Euclid, the Wide Field
Infrared Survey Telescope, the Square Kilometre Array, and the Next Generation
Very Large Array.Comment: 5 chapters, 160 pages, 107 figure
Daniel Devost
Age differences are derived between the various super star clusters of NGC 3690 using the two color diagram (B\GammaH) vs (H\GammaK) and previously published data on the physical properties of the gas. This method offers a quick and easy way to establish age differences down to a time resolution that is limited by the data on extinction. One of the infrared knots, suspected to be a galaxy nucleus, is found to be a starbursting region. The validity of the method is checked by comparing the equivalent width of the Hff line with the color maps of NGC 3690. 1. Introduction Although known to be very important in the evolution of galaxies, the star formation process is usually poorly accounted for in galactic evolution models. "Recipes" (e.g. Kennicutt 1998) are provided to account for the global characteristics of the star formation rate versus the interstellar medium (ISM); those are derived from the global or azimuthally averaged properties of observed galaxies while star formation is a ..