The Lyman-alpha reference sample (LARS) is a program with the Hubble Space Telescope (HST) that provides a sample of local universe laboratory galaxies in which to study the astrophysics of the visibility and strength of the Lyman-alpha (Lya) line of hydrogen. This article presents an overview of the survey, its selection function and HST imaging observations. The sample was selected from the GALEX+SDSS catalogue at z=0.028-0.19, in order to allow Lya to be captured with combinations of long pass filters in the Solar Blind Channel (SBC) of HST/ACS. In addition, LARS utilises Halpha and Hbeta narrow, and U, B, i broad-band imaging with ACS and WFC3. In order to study galaxies in which large numbers of Lya photons are produced we demanded an Halpha equivalent width > 100{\AA}. The sample of 14 galaxies covers far UV (FUV) luminosities that overlaps with those of high-z Lya emitters and Lyman Break Galaxies (LBGs). We present the reduction steps used to obtain the Lya images, including our LARS eXtraction software (LaXs) which utilises pixel-by-pixel spectral synthesis fitting to subtract the continuum at Lya. We demonstrate that the use of SBC long pass filters dramatically increase the signal to noise compared to the nominal Lya filter in SBC. To exemplify, we present results for Mrk 259. This irregular galaxy shows extended but strongly asymmetric Lya emission. Spectroscopy from HST/COS show a moderate outflow in the neutral ISM and an asymmetric Lya profile. Radiative transfer modeling is able to reproduce the Lya line profile, confirming the presence of an outflow. The integrated photometry provides a Lya luminosity of 1.3E42 erg/s an equivalent width W(Lya) =45{\AA} and a FUV absolute magnitude -19.2. Mrk 259 would hence be detectable in high-z Lya and LBG surveys. The total Lya escape fraction is 12%, similar to that observed at z>4. (shortened)
view Abstract Citations (106) References (74) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-Resolution Spectra of 24 Low-Redshift QSOs: The Properties of MG II Absorption Systems Tytler, David ; Boksenberg, A. ; Sargent, Wallace L. W. ; Young, Peter ; Kunth, Daniel Abstract High-resolution spectra of 245 low-redshift QSOs are presented, and Mg II emission-line equivalent widths and velocity widths are measured and briefly discussed. Improved statistical methods are presented for the extraction of significant absorption features from spectra. These techniques provide a simple and accurate estimate of the minimum equivalent widths which could be detected in any region of a spectrum. A search for Galactic Ca II in 13 lines of sight reveals five detections. Equivalent widths are in the range 0.2-0.3 A. Only three redshifted absorption systems were found, all dominated by Mg II 2796 A, 2803 A doublets. Mg(+)/Mg(0) and Mg(+)/Fe(+) values cannot be accounted for by collisional ionization alone. Factors determining the frequency of occurrence of Mg II systems are investigated using a composite sample of 14 systems from the spectra of 90 QSOs. Ten out of the 14 systems occur in five pairs of two systems each per QSO. The probability of these pairs being chance occurrences is only 0.0007. Publication: The Astrophysical Journal Supplement Series Pub Date: August 1987 DOI: 10.1086/191213 Bibcode: 1987ApJS...64..667T Keywords: Absorption Spectra; Magnesium; Quasars; Red Shift; Spectral Resolution; Abundance; Astronomical Spectroscopy; Atomic Interactions; Cosmology; Astrophysics; ATOMIC PROCESSES; COSMOLOGY; GALAXIES: INTERGALACTIC MEDIUM; INTERSTELLAR: ABUNDANCES; LINE IDENTIFICATIONS; QUASARS full text sources ADS | data products SIMBAD (90) NED (83)
In this letter we present the first results from a program aimed at measuring the stellar kinematics of blue compact galaxies by observing the near-infrared Calcium triplet. We show the first results for ESO 400-G43 based on deep VLT/FORS2 spectroscopy. The instabilities found in the central gaseous velocity field are not seen in the solid body stellar rotation curve, indicating that stars and gas are kinematically decoupled in this galaxy. Even if this galaxy has a perturbed gaseous velocity field, the stellar velocity dispersion on average agrees well with that derived from the nebular lines.
We present the results of a medium-resolution spectroscopic study of 142 Kiso ultraviolet-excess galaxies (KUGs), mostly of compact, irregular and interactive pair morphological types in the Kiso catalog. 137 objects are found to exhibit at least one emission line. The astrophysical implications of this survey will be discussed in a companion paper (Comte et al. 1994)
We present VLA HI imaging of the blue compact dwarf (BCD) galaxy Haro 2 and a map of its CO(1-0) distribution obtained with the OVRO millimeter array. In addition we obtained NIR JH images with the 2.1m telescope of Mexico's National Optical Observatory (OAN) and derived surface brightness profiles. Combining all these results we find an intriguing picture: the HI reveals that the kinematical major axis lies perpendicular to the photometric major axis. Our observations support the suggestion that this configuration is due to recent capture of an important quantity of gas of external origin.
Un echantillon de douze galaxies bleues compactes a ete observe avec le radiotelescope IRAM de 30 m pour tenter de detecter la transition rotationnelle J=1→0 de la molecule 12 CO. Aucune emission n'a ete decelee et les limites superieures de luminosites CO sont 8 fois plus faibles que celles realisees jusqu'a present. L'interpretation proposee suggere une deficience en CO, combinee a une emission optiquement fine a la frequence de la transition CO
We construct three extremely different scenarios of the star formation histories applicable to a sample of dwarf galaxies, based on either their present metallicity or their luminosity. The three possible scenarios imply different mechanical energy input rates, and these we compare with the theoretical lower limits established for the ejection of processed matter out of dwarf galaxies. The comparison strongly points to the existence of extended gaseous halos in these galaxies acting as the barrier that allows galaxies to retain their metals and enhance their abundance. At the same time, our findings strongly point to a continuous star-forming process, rather than to coeval bursts, as the main contributor to the overall metallicity in our galaxy sample.
We present Very Large Array H I imaging of two blue compact dwarf galaxies, Haro 2 and Haro 4, and of the spiral galaxy Haro 26, which is projected some 22' southwest of Haro 4. We also show a map of the CO(1–0) distribution of Haro 2 obtained with the Owens Valley Radio Observatory Millimeter Array, as well as derive an upper limit for CO(2–1) emission from Haro 4 obtained with the Caltech Submillimeter Observatory. The H I data of Haro 2 reveal that the kinematical major axis lies perpendicular to the photometric major axis, indicating that the atomic hydrogen rotates about the major axis of the galaxy. This confirms earlier indications based on CCD photometry that Haro 2 is a dust-lane dE rather than a dIrr. We propose that the present neutral and molecular ISM configuration is due to recent gas accretion or a merger. The H I distribution and dynamics of Haro 4 and the neighboring spiral Haro 26 suggest that they are currently undergoing a tidal interaction, reinforcing the notion that interactions play an important role in triggering the star formation witnessed in blue compact galaxies.
New integral field spectroscopy has been obtained for IZw 18, the nearby lowest-metallicity galaxy considered to be our best local analog of systems forming at high redshift (z). Here we report the spatially resolved spectral map of the nebular He ii λ4686 emission in IZw 18, from which we derived for the first time its total He ii-ionizing flux. Nebular He ii emission implies the existence of a hard radiation field. He ii-emitters are observed to be more frequent among high-z galaxies than for local objects. Therefore, investigating the He ii-ionizing source(s) in IZw 18 may reveal the ionization processes at high z. He ii emission in star-forming galaxies has been suggested to be mainly associated with Wolf–Rayet stars (WRs), but WRs cannot satisfactorily explain the He ii-ionization at all times, particularly at the lowest metallicities. Shocks from supernova remnants, or X-ray binaries, have been proposed as additional potential sources of He ii-ionizing photons. Our data indicate that conventional He ii-ionizing sources (WRs, shocks, X-ray binaries) are not sufficient to explain the observed nebular He iiλ4686 emission in IZw 18. We find that the He ii-ionizing radiation expected from models for either low-metallicity super-massive O stars or rotating metal-free stars could account for the He ii-ionization budget measured, while only the latter models could explain the highest values of He iiλ4686/Hβ observed. The presence of such peculiar stars in IZw 18 is suggestive and further investigation in this regard is needed. This letter highlights that some of the clues of the early universe can be found here in our cosmic backyard.
