Proceedings of the International Astronomical Union, 2012
ABSTRACT Lyman Break Analogs (LBAs) are a population of star-forming galaxies at low redshift (z ... more ABSTRACT Lyman Break Analogs (LBAs) are a population of star-forming galaxies at low redshift (z ˜ 0.2). These objects present metallicities, morphologies and other physical properties similar to higher redshift Lyman Break Galaxies (LBGs), motivating their detailed study as potential local analogs to high-redshift starburst galaxies (Hoopes et al. 2007, Basu-Zych et al. 2009, Overzier et al. 2010, Overzier et al. 2011).
Monthly Notices of the Royal Astronomical Society, 2014
ABSTRACT Lyman break analogues (LBAs) are a population of star-forming galaxies at low redshift (... more ABSTRACT Lyman break analogues (LBAs) are a population of star-forming galaxies at low redshift (z ~ 0.2) selected in the ultraviolet (UV). These objects present higher star formation rates and lower dust extinction than other galaxies with similar masses and luminosities in the local universe. In this work we present results from a survey with the Combined Array for Research in Millimetre-wave Astronomy (CARMA) to detect CO(1-0) emission in LBAs, in order to analyse the properties of the molecular gas in these galaxies. Our results show that LBAs follow the same Schmidt-Kennicutt law as local galaxies. On the other hand, they have higher gas fractions (up to 66%) and faster gas depletion time-scales (below 1 Gyr). These characteristics render these objects more akin to high-redshift star-forming galaxies. We conclude that LBAs are a great nearby laboratory for studying the cold interstellar medium in low-metallicity, UV-luminous compact star-forming galaxies.
X-ray emission from accreting binary systems (X-ray binaries) uniquely probe the binary phase of ... more X-ray emission from accreting binary systems (X-ray binaries) uniquely probe the binary phase of stellar evolution and the formation of compact objects such as neutron stars and black holes. A detailed understanding of X-ray binary systems is needed to provide physical insight into the formation and evolution of the stars involved, as well as the demographics of interesting binary remnants, such as millisecond pulsars and gravitational wave sources. Our program makes wide use of Chandra observations and complementary multiwavelength data sets (through, e.g., the Spitzer Infrared Nearby Galaxies Survey [SINGS] and the Great Observatories Origins Deep Survey [GOODS]), as well as super-computing facilities, to provide: (1) improved calibrations for correlations between X-ray binary emission and physical properties (e.g., star-formation rate and stellar mass) for galaxies in the local Universe; (2) new physical constraints on accreting binary processes (e.g., common-envelope phase and m...
Designed to study gamma ray bursts, the Swift satellite has also ultraviolet and optical capabili... more Designed to study gamma ray bursts, the Swift satellite has also ultraviolet and optical capabilities. In this study, we use the UVOT instrument aboard Swift to discover 1<z<2 Lyman break galaxies (LBGs). Using UVOT near-ultraviolet color selection, we select UV-dropouts in the Chandra Deep Field South (CDFS). We match the selected sources with available multi-wavelength data from ACS GOODS-South, MUSYC, and COMBO-17 to characterize spectral energy distributions and determine stellar masses, star formation rates (SFRs) and dust attenuation in these galaxies. Additionally, working with these multi-wavelength catalogs, we explore how the Swift UVOT selection of LBGs (and possibly the UV-dropout selection in general) might bias the final LBG sample. In this talk, I will present how the properties of the selected sample compare with other samples: z 3 LBGs, z<1 UV luminous galaxies, and other z=1-2 CDFS galaxies, and I will present the potential for using Swift to search for Ly...
We present early results from the deepest X-ray stacking of <5000 high redshift galaxies from ... more We present early results from the deepest X-ray stacking of <5000 high redshift galaxies from z=1 to 8 using the recently acquired Chandra Deep Field South (CDF-S) 4Ms data. The galaxy samples were selected using the Lyman break technique based on recent HST ACS and WFC3 observations. Based on the X-ray stacking analyses for the 1<zɜ LBGs, we find that the mean LX/SFR ratio remains roughly constant, consistent with X-ray binary population synthesis models. We do not obtain significant X-ray detections from stacking LBGs at z 6, 7, and 8 and obtain upper limits that are inconsistent with recently published results, constraining the SMBH accretion history of the Universe.
We find evidence that the high-mass X-ray binary (HMXB) populations in relatively metal- and dust... more We find evidence that the high-mass X-ray binary (HMXB) populations in relatively metal- and dust- poor UV-selected galaxies differs from those in other normal, local, star-forming galaxies, yielding higher 2-10 keV X-ray luminosities per star formation rate (SFR). Our metal and dust poor UV-selected galaxies are drawn from populations that span the majority of cosmic history -- ranging from Lyman break galaxies (LBGs) in the early Universe (z=1.5-4) to Lyman break analogs (LBAs) in the present-day Universe ( 0.1). Using X-ray stacking analyses of the 4 Ms Chandra Deep Field South (CDF-S) data with a sample of ~4000 z=1.5-4 LBGs, we find that the 2-10 keV X-ray luminosity per SFR (L_X/SFR) evolves mildly with redshift, consistent with predictions from X-ray binary population synthesis models. Additional Chandra observations of 6 relatively nearby ( 0.1) LBAs yield individual X-ray detections with elevated L_X/SFR ratios compared to local galaxies, but similar to the z>2 LBGs. In ...
ABSTRACT Studies of X-ray binary populations in galaxies allow us to gain insight into the key fa... more ABSTRACT Studies of X-ray binary populations in galaxies allow us to gain insight into the key factors contributing to the formation and evolution of compact objects, the stars involved in the accreting binary phase, and their associated remnants (e.g., millisecond pulsars and compact-object binaries). Early-type galaxies contain predominantly old stars (3-12 Gyr) and have X-ray emission dominated by low-mass X-ray binary (LMXB) populations. I will present results from deep Chandra and HST observations of three nearby early-type galaxies (NGC 3115, 3379, and 3384) that have luminosity-weighted stellar ages covering the range of ~3-10 Gyr. These data allow for the clean identification of field LMXB populations (i.e., sources not coincident with globular clusters), and provide unique measurements for how the field LMXB X-ray luminosity function evolves with time. Leading X-ray binary population synthesis models predict that field LMXB populations will be more prevalent and luminous in the younger early-type galaxies. For the first time, we can unambiguously confront these models and provide important new insight into the formation and evolution of LMXBs.
Supercompact ultraviolet-luminous galaxies (ScUVLGs), characterized by high far-UV luminosities a... more Supercompact ultraviolet-luminous galaxies (ScUVLGs), characterized by high far-UV luminosities and surface brightnesses as detected by GALEX, are intensely star-forming objects in the low-redshift universe (z 0.2), with star formation rates reaching up to 50 times that of the Milky Way. These objects present metallicities, morphologies and other physical properties similar to higher redshift Lyman-break galaxies (LBGs), motivating the detailed study
(Abridged) While the Swift satellite is primarily designed to study gamma-ray bursts, its ultravi... more (Abridged) While the Swift satellite is primarily designed to study gamma-ray bursts, its ultraviolet and optical imaging and spectroscopy capabilities are also being used for a variety of scientific programs. In this study, we use the UV/Optical Telescope (UVOT) instrument aboard Swift to discover 0.5<z<2 Lyman break galaxies (LBGs). UVOT has covered ~266 arcmin^2 at >60ks exposure time, achieving a limiting magnitude of u<24.5, in the Chandra Deep Field South (CDF-S). Applying UVOT near-ultraviolet color selection, we select 50 UV-dropouts from this UVOT CDF-S data. We match the selected sources with available multiwavelength data from GOODS-South, MUSYC, and COMBO-17 to characterize the spectral energy distributions for these galaxies and determine stellar masses, star formation rates (SFRs), and dust attenuations. We compare these properties for LBGs selected in this paper versus z~3 LBGs and other CDF-S galaxies in the same redshift range (0.5<z<2), identified using photometric redshift techniques. The z~1 LBGs have slightly lower stellar masses compared to z~3 LBGs and slightly higher stellar masses compared to the z~1 CDF-S galaxies. Similarly, our sample of z~1 LBGs has SFRs (derived using both ultraviolet and infrared data, where available) nearly an order of magnitude lower than z~3 LBGs but slightly higher than the comparison z~1 sample of CDF-S galaxies. We find that our z~1 UV-dropouts have A_FUV higher than z~3 LBGs, but is similar to the distribution of dust attenuations in the other CDF-S galaxies. Using the GOODS-South multiwavelength catalog of galaxies, we simulate a larger and fainter sample of LBGs to compare their properties with those of the UVOT-selected LBG sample. We conclude that UVOT can be useful for finding and studying the bright end of 0.5<z<2.0 LBGs.
Ultraviolet Luminous Galaxies have been identified as intensely star-forming, nearby galaxies -as... more Ultraviolet Luminous Galaxies have been identified as intensely star-forming, nearby galaxies -as local analogs to Lyman Break Galaxies. We investigate the radio properties of 46 compact UVLGs, along with ultraviolet observations and optical spectral data. Comparing the UV star formation rate to the star formation rate derived from the radio continuum, we find that these systems are underluminous in the radio; we detect only half of the UVLGs. We interpret this result in terms of both star formation history and dust content. Our analysis includes comparison samples of multiwavelength data from the First Look Survey and from the SDSS-GALEX matched catalogs. We conclude that compact UVLGs are young and show lower dust attenuation than average given their current rate of star formation.
Proceedings of the International Astronomical Union, 2012
ABSTRACT Lyman Break Analogs (LBAs) are a population of star-forming galaxies at low redshift (z ... more ABSTRACT Lyman Break Analogs (LBAs) are a population of star-forming galaxies at low redshift (z ˜ 0.2). These objects present metallicities, morphologies and other physical properties similar to higher redshift Lyman Break Galaxies (LBGs), motivating their detailed study as potential local analogs to high-redshift starburst galaxies (Hoopes et al. 2007, Basu-Zych et al. 2009, Overzier et al. 2010, Overzier et al. 2011).
Monthly Notices of the Royal Astronomical Society, 2014
ABSTRACT Lyman break analogues (LBAs) are a population of star-forming galaxies at low redshift (... more ABSTRACT Lyman break analogues (LBAs) are a population of star-forming galaxies at low redshift (z ~ 0.2) selected in the ultraviolet (UV). These objects present higher star formation rates and lower dust extinction than other galaxies with similar masses and luminosities in the local universe. In this work we present results from a survey with the Combined Array for Research in Millimetre-wave Astronomy (CARMA) to detect CO(1-0) emission in LBAs, in order to analyse the properties of the molecular gas in these galaxies. Our results show that LBAs follow the same Schmidt-Kennicutt law as local galaxies. On the other hand, they have higher gas fractions (up to 66%) and faster gas depletion time-scales (below 1 Gyr). These characteristics render these objects more akin to high-redshift star-forming galaxies. We conclude that LBAs are a great nearby laboratory for studying the cold interstellar medium in low-metallicity, UV-luminous compact star-forming galaxies.
X-ray emission from accreting binary systems (X-ray binaries) uniquely probe the binary phase of ... more X-ray emission from accreting binary systems (X-ray binaries) uniquely probe the binary phase of stellar evolution and the formation of compact objects such as neutron stars and black holes. A detailed understanding of X-ray binary systems is needed to provide physical insight into the formation and evolution of the stars involved, as well as the demographics of interesting binary remnants, such as millisecond pulsars and gravitational wave sources. Our program makes wide use of Chandra observations and complementary multiwavelength data sets (through, e.g., the Spitzer Infrared Nearby Galaxies Survey [SINGS] and the Great Observatories Origins Deep Survey [GOODS]), as well as super-computing facilities, to provide: (1) improved calibrations for correlations between X-ray binary emission and physical properties (e.g., star-formation rate and stellar mass) for galaxies in the local Universe; (2) new physical constraints on accreting binary processes (e.g., common-envelope phase and m...
Designed to study gamma ray bursts, the Swift satellite has also ultraviolet and optical capabili... more Designed to study gamma ray bursts, the Swift satellite has also ultraviolet and optical capabilities. In this study, we use the UVOT instrument aboard Swift to discover 1<z<2 Lyman break galaxies (LBGs). Using UVOT near-ultraviolet color selection, we select UV-dropouts in the Chandra Deep Field South (CDFS). We match the selected sources with available multi-wavelength data from ACS GOODS-South, MUSYC, and COMBO-17 to characterize spectral energy distributions and determine stellar masses, star formation rates (SFRs) and dust attenuation in these galaxies. Additionally, working with these multi-wavelength catalogs, we explore how the Swift UVOT selection of LBGs (and possibly the UV-dropout selection in general) might bias the final LBG sample. In this talk, I will present how the properties of the selected sample compare with other samples: z 3 LBGs, z<1 UV luminous galaxies, and other z=1-2 CDFS galaxies, and I will present the potential for using Swift to search for Ly...
We present early results from the deepest X-ray stacking of <5000 high redshift galaxies from ... more We present early results from the deepest X-ray stacking of <5000 high redshift galaxies from z=1 to 8 using the recently acquired Chandra Deep Field South (CDF-S) 4Ms data. The galaxy samples were selected using the Lyman break technique based on recent HST ACS and WFC3 observations. Based on the X-ray stacking analyses for the 1<zɜ LBGs, we find that the mean LX/SFR ratio remains roughly constant, consistent with X-ray binary population synthesis models. We do not obtain significant X-ray detections from stacking LBGs at z 6, 7, and 8 and obtain upper limits that are inconsistent with recently published results, constraining the SMBH accretion history of the Universe.
We find evidence that the high-mass X-ray binary (HMXB) populations in relatively metal- and dust... more We find evidence that the high-mass X-ray binary (HMXB) populations in relatively metal- and dust- poor UV-selected galaxies differs from those in other normal, local, star-forming galaxies, yielding higher 2-10 keV X-ray luminosities per star formation rate (SFR). Our metal and dust poor UV-selected galaxies are drawn from populations that span the majority of cosmic history -- ranging from Lyman break galaxies (LBGs) in the early Universe (z=1.5-4) to Lyman break analogs (LBAs) in the present-day Universe ( 0.1). Using X-ray stacking analyses of the 4 Ms Chandra Deep Field South (CDF-S) data with a sample of ~4000 z=1.5-4 LBGs, we find that the 2-10 keV X-ray luminosity per SFR (L_X/SFR) evolves mildly with redshift, consistent with predictions from X-ray binary population synthesis models. Additional Chandra observations of 6 relatively nearby ( 0.1) LBAs yield individual X-ray detections with elevated L_X/SFR ratios compared to local galaxies, but similar to the z>2 LBGs. In ...
ABSTRACT Studies of X-ray binary populations in galaxies allow us to gain insight into the key fa... more ABSTRACT Studies of X-ray binary populations in galaxies allow us to gain insight into the key factors contributing to the formation and evolution of compact objects, the stars involved in the accreting binary phase, and their associated remnants (e.g., millisecond pulsars and compact-object binaries). Early-type galaxies contain predominantly old stars (3-12 Gyr) and have X-ray emission dominated by low-mass X-ray binary (LMXB) populations. I will present results from deep Chandra and HST observations of three nearby early-type galaxies (NGC 3115, 3379, and 3384) that have luminosity-weighted stellar ages covering the range of ~3-10 Gyr. These data allow for the clean identification of field LMXB populations (i.e., sources not coincident with globular clusters), and provide unique measurements for how the field LMXB X-ray luminosity function evolves with time. Leading X-ray binary population synthesis models predict that field LMXB populations will be more prevalent and luminous in the younger early-type galaxies. For the first time, we can unambiguously confront these models and provide important new insight into the formation and evolution of LMXBs.
Supercompact ultraviolet-luminous galaxies (ScUVLGs), characterized by high far-UV luminosities a... more Supercompact ultraviolet-luminous galaxies (ScUVLGs), characterized by high far-UV luminosities and surface brightnesses as detected by GALEX, are intensely star-forming objects in the low-redshift universe (z 0.2), with star formation rates reaching up to 50 times that of the Milky Way. These objects present metallicities, morphologies and other physical properties similar to higher redshift Lyman-break galaxies (LBGs), motivating the detailed study
(Abridged) While the Swift satellite is primarily designed to study gamma-ray bursts, its ultravi... more (Abridged) While the Swift satellite is primarily designed to study gamma-ray bursts, its ultraviolet and optical imaging and spectroscopy capabilities are also being used for a variety of scientific programs. In this study, we use the UV/Optical Telescope (UVOT) instrument aboard Swift to discover 0.5<z<2 Lyman break galaxies (LBGs). UVOT has covered ~266 arcmin^2 at >60ks exposure time, achieving a limiting magnitude of u<24.5, in the Chandra Deep Field South (CDF-S). Applying UVOT near-ultraviolet color selection, we select 50 UV-dropouts from this UVOT CDF-S data. We match the selected sources with available multiwavelength data from GOODS-South, MUSYC, and COMBO-17 to characterize the spectral energy distributions for these galaxies and determine stellar masses, star formation rates (SFRs), and dust attenuations. We compare these properties for LBGs selected in this paper versus z~3 LBGs and other CDF-S galaxies in the same redshift range (0.5<z<2), identified using photometric redshift techniques. The z~1 LBGs have slightly lower stellar masses compared to z~3 LBGs and slightly higher stellar masses compared to the z~1 CDF-S galaxies. Similarly, our sample of z~1 LBGs has SFRs (derived using both ultraviolet and infrared data, where available) nearly an order of magnitude lower than z~3 LBGs but slightly higher than the comparison z~1 sample of CDF-S galaxies. We find that our z~1 UV-dropouts have A_FUV higher than z~3 LBGs, but is similar to the distribution of dust attenuations in the other CDF-S galaxies. Using the GOODS-South multiwavelength catalog of galaxies, we simulate a larger and fainter sample of LBGs to compare their properties with those of the UVOT-selected LBG sample. We conclude that UVOT can be useful for finding and studying the bright end of 0.5<z<2.0 LBGs.
Ultraviolet Luminous Galaxies have been identified as intensely star-forming, nearby galaxies -as... more Ultraviolet Luminous Galaxies have been identified as intensely star-forming, nearby galaxies -as local analogs to Lyman Break Galaxies. We investigate the radio properties of 46 compact UVLGs, along with ultraviolet observations and optical spectral data. Comparing the UV star formation rate to the star formation rate derived from the radio continuum, we find that these systems are underluminous in the radio; we detect only half of the UVLGs. We interpret this result in terms of both star formation history and dust content. Our analysis includes comparison samples of multiwavelength data from the First Look Survey and from the SDSS-GALEX matched catalogs. We conclude that compact UVLGs are young and show lower dust attenuation than average given their current rate of star formation.
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