SBS0335-052 (Z simeq 141 Z_) is a dwarf star-forming galaxy that together with IZw18 holds the re... more SBS0335-052 (Z simeq 141 Z_) is a dwarf star-forming galaxy that together with IZw18 holds the record of the lowest metallicity ever observed in the local Universe. A wealth of observational evidence supports the hypothesis that this target is in fact a nearbyprimordial galaxy, contrary to what observationally demonstrated, e.g. for IZw18. However, no conclusive results are available at present. A new (and probably only viable) approach in order to establish the real nature of SBS0335-052 young or old galaxy) is represented by FUSE observations. FUSE gives us access to the richness of interstellar absorption lines arising from the neutral interstellar medium (ISM) of this galaxy in the FUV spectral range. We propose to obtain high SN FUSE spectra of SBS0335-052 in order to estimate column densities of the most common ions and derive the metal content of the neutral ISM with unprecedented accuracy (lesssim .15 dex). In these extremely metal-poor systems, the neutral ISM dominates the baryonic mass, and can hide the bulk of the metals produced by the galaxy during a lifetime. The relative abundances of metals which originate in different types of stars are also like a fossil record of the past star-formation (SF) history, the neutral gas tracing a more ancient past than the ionized gas in the HII regions due to larger timescales of the mixing processes that come into play. Inferring the metal content of the neutral ISM in SBS0335-052 will give us access to its ancient gtrsim 1 Gyr) SF history and will allow us to assess or reject its primordial nature, investigate its connection with the high-redshift Universe (e.g., Lyman Break Galaxies, Damped Lyalpha systems), and put strong constraints on theories of galaxy formation and evolution. Independently of the real nature of SBS0335-052, the proposed FUSE spectra will constitute an invaluable complement to the Spitzer data of this galaxy which shows a very peculiar mid-infrared spectrum.
We present results from a FUSE survey of local starburst galaxies. We combine ongoing observation... more We present results from a FUSE survey of local starburst galaxies. We combine ongoing observations from the FUSE Starburst Legacy Project with archival observations to create the largest sample to date ( 50) of far-ultraviolet (FUV) galaxy spectra. In contrast to the local universe where observations of galaxies in the FUV are limited by atmospheric absorption, relatively large samples of star forming galaxies have been observed at high redshifts. Rest wavelength FUV observations of Lyman break galaxies (LBGs) provide important insights into galaxy formation and evolution. The FUV wavelength regime is rich in absorption features that probe the characteristics of galactic outflows, the inter-stellar medium (ISM), and stellar content. FUV observations can help constrain outflow velocities, energetics, and the chemical composition of galactic outflows. Outflows from LBGs also play a role in reionizing the universe and enriching the IGM. Our sample provides an important benchmark to compare LBGs to our local galaxy population. The proximity of our galaxies also allows us to assemble a complimentary multiwavelength (e.g. X-ray) data set that is not possible at high redshifts. Preliminary results from our study include evidence that the outflow speeds of neutral and low ionization lines increase with the star formation rate (SFR). The OVI absorption line is also significantly broader and more blueshifted than the lower ionization lines. This is consistent with OVI production at the interface between the hot outrushing gas and the cooler ions. These results show that our study provides a unique view of starburst galaxies that will play an important role in constraining galaxy formation and evolution.
Proceedings of the International Astronomical Union, 2007
IZw18 is one of the most interesting external galaxies. It is the most metal poor galaxy ever dis... more IZw18 is one of the most interesting external galaxies. It is the most metal poor galaxy ever discovered (metallicity roughly 1/50 of solar), hence the least evolved one; thus providing fundamental information on the primordial chemical abundances and on the evolution of primordial galaxies. It is a dwarf galaxy, hence a possible prototype of the systems suggested to contribute as building blocks to the formation of massive galaxies, and a benchmark to study the effects of SN explosions on the ISM of systems with low potential well. If a metal poor galaxy is young, one may think that simply its stars haven't had time to chemically enrich the medium; but if it is old, other mechanisms to reduce the metals need to be invoked; galactic winds triggered by SN explosions being currently the favoured ones. IZw18 is at a relative short distance (12-15 Mpc) and therefore resolvable in its individual stars with the Hubble Space Telescope (HST). Yet, its age and its distance are still subjects of hot debates. IZw18 has been recurrently claimed to be a genuinely young system, with a star formation activity started only recently; however, everytime we have been able to look deeper in its images with high-res photometry, we have succesfully resolved stars increasingly older. Ten years ago IZw18 was claimed to be less than 50 Myr old, but subsequent careful analyses of its stars, resolved with HST's WFPC2 and NICMOS, showed that objects at least several hundreds Myr old are present. Two years ago, new HST-ACS data led to a press-release indicating 500 Myr as the oldest possible age of IZw18; yet, again, more careful analyses of these data show that red giants are likely to be present, implying an age of at least 2 Gyr. Here, we will discuss the existing photometry and present an ongoing HST-ACS project which will allow us to precisely derive the galaxy distance, by studying its Cepheid variables, and firmly establish the age of its faintest resolved populations.
We present the far-UV spectroscopic study of the giant H II region NGC604 in the dwarf spiral gal... more We present the far-UV spectroscopic study of the giant H II region NGC604 in the dwarf spiral galaxy M33. Neutral hydrogen and many metal lines are observed in absorption against the continuum given by the young massive stars embedded in the ionized gas. From profile fitting, we determine the abundances in the diffuse neutral gas and compare them with the ionized gas values. We find that nitrogen, oxygen, argon and iron are underabundant in the neutral phase by a factor of ˜6. This could either be explained by the presence of less chemically evolved gas pockets in the sightlines or by dense clouds out of which H II regions form. Those could be more metallic than the diffuse medium.
We propose to observe 2 of the most metal-poor (Z lesssim 120 solar) star-forming dwarf galaxies ... more We propose to observe 2 of the most metal-poor (Z lesssim 120 solar) star-forming dwarf galaxies in the local Universe considered to represent the nearby counterpart of primeval galaxies at high redshift, SBS0335-052 and SBS1415+437. In these systems the neutral phase of the interstellar medium (ISM) dominates the baryonic mass, and can hide the bulk of the metals. Determining the metal content of the neutral ISM is thus of fundamental importance to infer the chemical evolutionary state of this class of objects, assess or reject their primordial nature, investigate their connection with the high-redshift Universe (e.g., Lyman Break Galaxies and Damped Lyalpha Systems), and better understand galaxy formation and evolution. The high resolution, sensitivity, and spectral range of FUSE is mandatory. The FUV absorption lines in the very blue spectra of these star-forming galaxies will allow us to derive with an accuracy lesssim 0.1 dex the metal content in the neutral gas by simply adopting the same multi-component fitting technique widely used to study QSO absorption systems. Our pilot study on the FUSE archival data of IZw18, the most metal-poor (Z simeq 150 solar) galaxy known so far in the local Universe, has demonstrated the feasibility of the project, and has brought us to the following exciting discovery. The Hsc i in IZw18 is already enriched in metals, and a certain amount of ancient (gtrsim Gyr) star formation is required prior to the more recent activity responsible for the additional enrichment of the Hsc ii regions. The new FUSE observations of SBS0335-052 and SBS1415+437 will allow us to assess if the behavior of IZw18 is common or an exception for this class of objects.
We will observe the flux standard G191B2B,obtaining echelle spectra in all primary and intermedia... more We will observe the flux standard G191B2B,obtaining echelle spectra in all primary and intermediate wavelength settings. While this was done in cycle 10 {8915}, the echelle blaze shift has proved to depend sensitively on side of operation, time and the exact MSM positioning. We therefore believe it is important to obtain a complete set of post-repair data at default MSM position to allow a comprehensive solution for the echelle blaze shifts on a repaired side 2.;
SBS0335-052 (Z simeq 141 Z_) is a dwarf star-forming galaxy that together with IZw18 holds the re... more SBS0335-052 (Z simeq 141 Z_) is a dwarf star-forming galaxy that together with IZw18 holds the record of the lowest metallicity ever observed in the local Universe. A wealth of observational evidence supports the hypothesis that this target is in fact a nearbyprimordial galaxy, contrary to what observationally demonstrated, e.g. for IZw18. However, no conclusive results are available at present. A new (and probably only viable) approach in order to establish the real nature of SBS0335-052 young or old galaxy) is represented by FUSE observations. FUSE gives us access to the richness of interstellar absorption lines arising from the neutral interstellar medium (ISM) of this galaxy in the FUV spectral range. We propose to obtain high SN FUSE spectra of SBS0335-052 in order to estimate column densities of the most common ions and derive the metal content of the neutral ISM with unprecedented accuracy (lesssim .15 dex). In these extremely metal-poor systems, the neutral ISM dominates the baryonic mass, and can hide the bulk of the metals produced by the galaxy during a lifetime. The relative abundances of metals which originate in different types of stars are also like a fossil record of the past star-formation (SF) history, the neutral gas tracing a more ancient past than the ionized gas in the HII regions due to larger timescales of the mixing processes that come into play. Inferring the metal content of the neutral ISM in SBS0335-052 will give us access to its ancient gtrsim 1 Gyr) SF history and will allow us to assess or reject its primordial nature, investigate its connection with the high-redshift Universe (e.g., Lyman Break Galaxies, Damped Lyalpha systems), and put strong constraints on theories of galaxy formation and evolution. Independently of the real nature of SBS0335-052, the proposed FUSE spectra will constitute an invaluable complement to the Spitzer data of this galaxy which shows a very peculiar mid-infrared spectrum.
We present results from a FUSE survey of local starburst galaxies. We combine ongoing observation... more We present results from a FUSE survey of local starburst galaxies. We combine ongoing observations from the FUSE Starburst Legacy Project with archival observations to create the largest sample to date ( 50) of far-ultraviolet (FUV) galaxy spectra. In contrast to the local universe where observations of galaxies in the FUV are limited by atmospheric absorption, relatively large samples of star forming galaxies have been observed at high redshifts. Rest wavelength FUV observations of Lyman break galaxies (LBGs) provide important insights into galaxy formation and evolution. The FUV wavelength regime is rich in absorption features that probe the characteristics of galactic outflows, the inter-stellar medium (ISM), and stellar content. FUV observations can help constrain outflow velocities, energetics, and the chemical composition of galactic outflows. Outflows from LBGs also play a role in reionizing the universe and enriching the IGM. Our sample provides an important benchmark to compare LBGs to our local galaxy population. The proximity of our galaxies also allows us to assemble a complimentary multiwavelength (e.g. X-ray) data set that is not possible at high redshifts. Preliminary results from our study include evidence that the outflow speeds of neutral and low ionization lines increase with the star formation rate (SFR). The OVI absorption line is also significantly broader and more blueshifted than the lower ionization lines. This is consistent with OVI production at the interface between the hot outrushing gas and the cooler ions. These results show that our study provides a unique view of starburst galaxies that will play an important role in constraining galaxy formation and evolution.
Proceedings of the International Astronomical Union, 2007
IZw18 is one of the most interesting external galaxies. It is the most metal poor galaxy ever dis... more IZw18 is one of the most interesting external galaxies. It is the most metal poor galaxy ever discovered (metallicity roughly 1/50 of solar), hence the least evolved one; thus providing fundamental information on the primordial chemical abundances and on the evolution of primordial galaxies. It is a dwarf galaxy, hence a possible prototype of the systems suggested to contribute as building blocks to the formation of massive galaxies, and a benchmark to study the effects of SN explosions on the ISM of systems with low potential well. If a metal poor galaxy is young, one may think that simply its stars haven't had time to chemically enrich the medium; but if it is old, other mechanisms to reduce the metals need to be invoked; galactic winds triggered by SN explosions being currently the favoured ones. IZw18 is at a relative short distance (12-15 Mpc) and therefore resolvable in its individual stars with the Hubble Space Telescope (HST). Yet, its age and its distance are still subjects of hot debates. IZw18 has been recurrently claimed to be a genuinely young system, with a star formation activity started only recently; however, everytime we have been able to look deeper in its images with high-res photometry, we have succesfully resolved stars increasingly older. Ten years ago IZw18 was claimed to be less than 50 Myr old, but subsequent careful analyses of its stars, resolved with HST's WFPC2 and NICMOS, showed that objects at least several hundreds Myr old are present. Two years ago, new HST-ACS data led to a press-release indicating 500 Myr as the oldest possible age of IZw18; yet, again, more careful analyses of these data show that red giants are likely to be present, implying an age of at least 2 Gyr. Here, we will discuss the existing photometry and present an ongoing HST-ACS project which will allow us to precisely derive the galaxy distance, by studying its Cepheid variables, and firmly establish the age of its faintest resolved populations.
We present the far-UV spectroscopic study of the giant H II region NGC604 in the dwarf spiral gal... more We present the far-UV spectroscopic study of the giant H II region NGC604 in the dwarf spiral galaxy M33. Neutral hydrogen and many metal lines are observed in absorption against the continuum given by the young massive stars embedded in the ionized gas. From profile fitting, we determine the abundances in the diffuse neutral gas and compare them with the ionized gas values. We find that nitrogen, oxygen, argon and iron are underabundant in the neutral phase by a factor of ˜6. This could either be explained by the presence of less chemically evolved gas pockets in the sightlines or by dense clouds out of which H II regions form. Those could be more metallic than the diffuse medium.
We propose to observe 2 of the most metal-poor (Z lesssim 120 solar) star-forming dwarf galaxies ... more We propose to observe 2 of the most metal-poor (Z lesssim 120 solar) star-forming dwarf galaxies in the local Universe considered to represent the nearby counterpart of primeval galaxies at high redshift, SBS0335-052 and SBS1415+437. In these systems the neutral phase of the interstellar medium (ISM) dominates the baryonic mass, and can hide the bulk of the metals. Determining the metal content of the neutral ISM is thus of fundamental importance to infer the chemical evolutionary state of this class of objects, assess or reject their primordial nature, investigate their connection with the high-redshift Universe (e.g., Lyman Break Galaxies and Damped Lyalpha Systems), and better understand galaxy formation and evolution. The high resolution, sensitivity, and spectral range of FUSE is mandatory. The FUV absorption lines in the very blue spectra of these star-forming galaxies will allow us to derive with an accuracy lesssim 0.1 dex the metal content in the neutral gas by simply adopting the same multi-component fitting technique widely used to study QSO absorption systems. Our pilot study on the FUSE archival data of IZw18, the most metal-poor (Z simeq 150 solar) galaxy known so far in the local Universe, has demonstrated the feasibility of the project, and has brought us to the following exciting discovery. The Hsc i in IZw18 is already enriched in metals, and a certain amount of ancient (gtrsim Gyr) star formation is required prior to the more recent activity responsible for the additional enrichment of the Hsc ii regions. The new FUSE observations of SBS0335-052 and SBS1415+437 will allow us to assess if the behavior of IZw18 is common or an exception for this class of objects.
We will observe the flux standard G191B2B,obtaining echelle spectra in all primary and intermedia... more We will observe the flux standard G191B2B,obtaining echelle spectra in all primary and intermediate wavelength settings. While this was done in cycle 10 {8915}, the echelle blaze shift has proved to depend sensitively on side of operation, time and the exact MSM positioning. We therefore believe it is important to obtain a complete set of post-repair data at default MSM position to allow a comprehensive solution for the echelle blaze shifts on a repaired side 2.;
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