Blue Compact Galaxies Research Articles

H i studies of extremely metal-deficient galaxies - II. Giant Metrewave Radio Telescope observations of SBS 1129+576

We present Giant Metrewave Radio Telescope H i observations of an extremely metal-deficient galaxy SBS 1129+576. SBS 1129+576 has a weighted mean oxygen abundance of 12 + log (O/H) = 7.41 ± 0.07, or 1/18 of the solar value. Our H i observations show that the galaxy is strongly interacting with a companion (projected separation ~ 27 kpc) galaxy, SBS 1129+577. HI emission from a third, smaller galaxy, SDSS J113227.68+572142.3, is also present in the data cube. We study the HI morphology and kinematics of this small group at angular resolutions ranging from ~ 40 to 8 arcsec. The low-resolution map shows a bridge of emission connecting the two larger galaxies and a large one-armed spiral distortion of the disc of SBS 1129+577. We measure HI masses of ~ 4.2 × 10 8 , ~ 2.7 × 10 9 and ~ 2.1 × 10 8 M ⊙ for SBS 1129+576, SBS 1129+577 and the gas in the bridge, respectively. Assuming that most of the bridge gas originally came from SBS 1129+576, approximately one-third of its original gas mass has been stripped off. The third smaller galaxy has an H i mass of (M HI ~ 1.1 × 10 7 M ⊙ ) and does not show any sign of interaction with the other two galaxies. The higher-resolution maps show that SBS 1129+577 has a central bar and a ring surrounding the bar; there is also a hint of an integral-shaped warp in SBS 1129+576. All these features are very likely to have been induced by the tidal interaction. In both SBS 1129+576 and SBS 1129+577, there is, in general, a good correspondence between regions with high H i column density and those with ongoing star formation. The two brightest H ii regions in SBS 1129+576 have (inclination-corrected) gas column densities of ~ 1.6 × 10 21 and ~ 1.8 × 10 21 atoms cm -2 , respectively. The inclination-corrected H i column density near the H ii regions in SBS 1129+577 is generally above ~ 2.0 × 10 21 atoms cm −2 . These values are close to the threshold density for star formation observed in other blue compact galaxies. In contrast to SBS 1129+576 and SBS 1129+577 which are very gas-rich, the third member of this group, SDSS J113227.68+572142.3, is gas-poor.

The N/O Plateau of Blue Compact Galaxies: Monte Carlo Simulations of the Observed Scatter

Chemical evolution models and Monte Carlo simulation techniques have been combined for the first time to study the distribution of blue compact galaxies on the N/O plateau. Each simulation comprises 70 individual chemical evolution models. For each model, input parameters relating to a galaxy's star formation history (bursting or continuous star formation, star formation efficiency), galaxy age, and outflow rate are chosen randomly from ranges predetermined to be relevant. Predicted abundance ratios from each simulation are collectively overplotted onto the data to test its viability. We present our results both with and without observational scatter applied to the model points. Our study shows that most trial combinations of input parameters, including a simulation comprising only simple models with instantaneous recycling, are successful in reproducing the observed morphology of the N/O plateau once observational scatter is added. Therefore simulations which include delay of nitrogen injection are no longer favored over those which propose that most nitrogen is produced by massive stars, if only the plateau morphology is used as the principal constraint. The one scenario which clearly cannot explain plateau morphology is one in which galaxy ages are allowed to range below 250 Myr. We conclude that the present data for the N/O plateau are insufficient by themselves for identifying the portion of the stellar mass spectrum most responsible for cosmic nitrogen production.

Edge-on Low Surface Brightness Galaxies in the SDSS and the Red Halo Phenomenon

AbstractExtremely red halos have been detected around high surface brightness (HSB) disk galaxies and blue compact galaxies. We analyse the halo emission of a sample of 970 stacked edge-on low surface brightness (LSB) galaxies in the SDSS (DR4) down to μg ~ 30 mag arcsec−2. These are divided by g − r colour limits into a “blue” Sample A (336 galaxies), “yellow” Sample B (318 galaxies) and “red” Sample C (316 galaxies). The gri colours indicate a prominent red excess in the polar direction, strongly deviating from any normal stellar population.

The Kinematics of Extended Hα Emission in Blue Compact Galaxies

AbstractBlue Compact Galaxies (BCGs) have received interest mainly because they comprise the best available test-beds for studies of low-metallicity star formation (SF) and allow the study of relatively unevolved systems at low redshift. Their ongoing phase of intense star formation is a transient phenomenon and the best candidates for its trigger are interactions and mergers. Studies of the kinematics are important for the understanding of this process.We present spatially resolved kinematics from the Hα line in five BCGs that show an extended region of ionised emission around the central starburst. We find this region to have near-spherical isophotes at large radii and to be dynamically decoupled from a central disturbance. A scenario where the strong triggered star formation in the center ionises the surrounding gas cloud, still following its original motions, can qualitatively explain these common features. The poster, including the figures, can be found at http://kern-2pt/thomasmarquart.net/pspdf/prague-marquart.pdf.

The Red Halos of Galaxies

AbstractOptical and near-IR surface photometry of the halos of disk galaxies and blue compact galaxies have revealed a very red spectral energy distribution, which cannot easily be reconciled with any normal type of stellar population. Using spectral evolutionary models, we demonstrate that a stellar population with an extremely bottom-heavy initial mass function can explain the red halos of both types of objects. Because of its very high mass-to-light ratio, this halo population may account for some of the missing baryons in the local Universe.

Detection of Escaping Lyman Continuum Radiation in Two Local Starbursts Using FUSE

AbstractWe present the detection of escaping Lyman Continuum (LyC) radiation from two local starburst galaxies, Tol 1247-232 and Tol 0440-381, using archival data from the Far Ultraviolet Spectroscopic Explorer (FUSE). From profile fitting of metal lines, high densities of neutral gas were derived for both galaxies, implying that the LyC radiation is escaping from holes in the interstellar medium. The first results for one of the galaxies, Tol 1247-232, give an escape fraction (fesc) of 17–35%. These new detections, together with that of the blue compact galaxy Haro 11 in Bergvall et al. (2006) where fesc between 4–10% was found, will have a feedback on cosmic reionization models.

Ar III]/[O III] and [S III]/[O III]: well-behaved oxygen abundance indicators for HII regions and star forming galaxies

We propose two statistical methods to derive oxygen abundances in HII regions and star forming galaxies and calibrate them with a sample of several hundred giant HII regions in spiral and blue compact galaxies as well as of galaxies from the Sloan Digital Sky Survey. We show the advantages of our new abundance indicators over previous ones.

The Star Formation History of the Disk of the Starburst Galaxy M82

Spectroscopic, photometric, and dynamical data of the inner 3 kpc of the starburst galaxy M82 are analyzed in order to investigate the star formation history of its disk. The long-slit spectra along the major axis are dominated by Balmer absorption lines in the region outside the nuclear starburst all the way up to ≈3.5 scale-lengths (μB = 22 mag arcsec-2). Single stellar population (SSP) spectra of age 0.4-1.0 Gyr match the observed spectra in the 1-3 kpc zone well, with a marginally higher mean age of the stellar population in the outer parts. The mass in these populations, along with that in the gas component, makes up for the inferred dynamical mass in the same annular zone for a Kroupa initial mass function, with a low-mass cutoff of ml = 0.4 M☉. The observed ratio of the abundances of α-elements with respect to Fe is also consistent with the idea that almost all the stars in the M82 disk formed in a burst of short duration (0.3 Gyr) around 0.8 Gyr ago. We find that the optical/near-infrared colors and their gradients in the disk are determined by the reddening, with visual extinction exceeding 1 mag even in the outer parts of the disk, where there is apparently no current star formation. The disk-wide starburst activity was most likely triggered by the interaction of M82 with its massive neighbor M81, around 1 Gyr ago. The properties of the disk of M82 very much resemble the properties of the disks of luminous compact blue galaxies seen at z = 0.2-1.0.

Luminous Compact Blue Galaxies up to z ~ 1 in the Hubble Space Telescope Ultra Deep Field. I. Small Galaxies or Blue Centers of Massive Disks?

We analyze 26 luminous compact blue galaxies (LCBGs) in the Hubble Space Telescope ACS Ultra Deep Field (UDF) at z ~ 0.2-1.3, to determine whether these truly are small galaxies or, rather, bright central starbursts within existing or forming large disk galaxies. Surface brightness profiles from UDF images reach fainter than rest-frame 26.5 B mag arcsec-2 even for compact objects at z ~ 1. Most LCBGs show a smaller, brighter component that is likely star-forming, and an extended, roughly exponential component with colors suggesting stellar ages from ≳100 Myr to a few gigayears. Scale lengths of the extended components are mostly ≲2 kpc, more than 1.5-2 times smaller than those of nearby large disk galaxies like the Milky Way. Larger, very low surface brightness disks can be excluded down to faint rest-frame surface brightnesses (≳26 B mag arcsec-2). However, one or two of the LCBGs are large, disklike galaxies that meet LCBG selection criteria because of a bright central nucleus, possibly a forming bulge. These results indicate that ≳90% of high-z LCBGs are small galaxies that will evolve into small disk galaxies, or low-mass spheroidal or irregular galaxies in the local universe, assuming passive evolution and no significant disk growth. The data do not reveal signs of disk formation around small, H II galaxy-like LCBGs, nor do they suggest a simple inside-out growth scenario for larger LCBGs with a disklike morphology. Irregular blue emission in distant LCBGs is relatively extended, suggesting that nebular emission lines from star-forming regions sample a major fraction of an LCBG's velocity field.

First detection of Lyman continuum escape from a local starburst galaxy

Context: The dominating reionization source in the young universe has not yet been identified. Possible candidates include metal poor dwarf galaxies with starburst properties.Aims. We selected an extreme starburst dwarf, the Blue Compact Galaxy Haro 11, with the aim of determining the Lyman continuum escape fraction from UV spectroscopy.Methods. Spectra of Haro 11 were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). A weak signal shortwards of the Lyman break is identified as Lyman continuum (LyC) emission escaping from the ongoing starburst. From profile fitting to weak metal lines we derive column densities of the low ionization species. Adopting a metallicity typical of the H II regions of Haro 11, these data correspond to a hydrogen column density of ~10^19cm^-2. This relatively high value indicates that most of the LyC photons escape through transparent holes in the interstellar medium. We then use spectral evolutionary models to constrain the escape fraction of the produced LyC photons.Results. Assuming a normal Salpeter initial mass function we obtain a Lyman continuum escape fraction of f_esc˜ 4-10%. We argue that in a hierarchical galaxy formation scenario, the upper limit we derive for the escape rate allows for a substantial contribution to cosmic reionization by starburst dwarf galaxies at high redshifts.

The impact of the visibility of the [O iii]λ4363 line on the general properties of H ii galaxies in the Local Universe

We present a statistical study of a very large sample of HII galaxies taken from the literature. We focus on the differences in several properties between galaxies that show the auroral line [OIII]λ4363 and those that do not present this feature in their spectra. It turns out that objects without this auroral line are more luminous, more metal-rich and present a lower ionization degree. The underlying population is found to be much more important for objects without the [OIII]λ4363 line, and the effective temperature of the ionizing star clusters of galaxies not showing the auroral line is probably lower. We also study the subsample of HII galaxies whose properties most closely resemble the properties of the intermediate-redshift population of Luminous Compact Blue Galaxies (LCBGs). The objects from this subsample are more similar to the objects not showing the [OIII]λ4363 line. It might therefore be expected that the intermediate-redshift population of LCBGs is powered by very massive, yet somewhat aged star clusters. The oxygen abundance of LCBGs would be greater than the average oxygen abundance of local HII galaxies.

Morphology and Evolution of Emission‐Line Galaxies in the Hubble Ultra Deep Field

We investigate the properties and evolution of a sample of galaxies selected to have prominent emission lines in low-resolution grism spectra of the Hubble Ultra Deep Field (HUDF). These objects, eGRAPES, are late type blue galaxies, characterized by small proper sizes (R_50 < 2 kpc) in the 4350A rest-frame, low masses (5x10^9 M_sun), and a wide range of luminosities and surface brightnesses. The masses, sizes and volume densities of these objects appear to change very little up to a redshift of z=1.5. On the other hand, their surface brightness decreases significantly from z=1.5 to z=0 while their mass-to-light ratio increases two-folds. This could be a sign that most of low redshift eGRAPES have an older stellar population than high redshift eGRAPES and hence that most eGRAPES formed at higher redshifts. The average volume density of eGRAPES is (1.8 \pm 0.3)x10^{-3} Mpc^{-3} between 0.3 < z < 1.5. Many eGRAPES would formally have been classified as Luminous Compact Blue Galaxies (LCBGs) if these had been selected based on small physical size, blue intrinsic color, and high surface brightness, while the remainder of the sample discussed in this paper forms an extension of LCBGs towards fainter luminosities.

Luminous Compact Blue Galaxies in Intermediate-Redshift Galaxy Clusters: A Significant but Extreme Butcher-Oemler Population

We identify a population of luminous compact blue galaxies (LCBGs) in two galaxy clusters: MS 0451.6-0305 (z = 0.54) and Cl 1604+4304 (z = 0.9). LCBGs are identified via photometric characteristics and photometric redshifts derived from broad- and narrowband images taken with the WIYN telescope and the Hubble Space Telescope (HST). We analyze their surface densities and clustering properties to find that they compose a statistically significant portion (42% and 53%, respectively) of the Butcher-Oemler (BO) galaxies in both clusters and that their spatial distributions are best characterized by a shell model. The enhancement of the projected space density of LCBGs with MB < -18.5 in the clusters relative to the field is 3-10 times higher than the BO population as a whole but 2 times lower than the red population, except in the core where LCBGs are absent. Assuming some fading, a natural descendant would be small, low-luminosity galaxies found preferentially in today's clusters, such as dE galaxies.

The DEEP2 Galaxy Redshift Survey: Discovery of Luminous, Metal-poor Star-forming Galaxies at Redshifts z ~ 0.7

We have discovered a sample of 17 metal-poor, yet luminous, star-forming galaxies at redshifts z ~ 0.7. They were selected from the initial phase of the DEEP2 survey of 3900 galaxies and the Team Keck Redshift Survey (TKRS) of 1536 galaxies as those showing the temperature-sensitive [O III] λ4363 auroral line. These rare galaxies have blue luminosities close to L*, high star formation rates of 5-12 M☉ yr-1, and oxygen abundances of 1/3 to 1/10 solar. They thus lie significantly off the luminosity-metallicity relation found previously for field galaxies with strong emission lines at redshifts z ~ 0.7. The prior surveys relied on indirect, empirical calibrations of the R23 diagnostic and the assumption that luminous galaxies are not metal-poor. Our discovery suggests that this assumption is sometimes invalid. As a class, these newly discovered galaxies are (1) more metal-poor than common classes of bright emission-line galaxies at z ~ 0.7 or at the present epoch; (2) comparable in metallicity to z ~ 3 Lyman break galaxies but less luminous; and (3) comparable in metallicity to local metal-poor extreme blue compact galaxies (XBCGs), but more luminous. Together, the three samples suggest that the most luminous, metal-poor, compact galaxies become fainter over time.

The Hamburg/SAO survey for emission-line galaxies

We present the sixth list with results of the Hamburg/SAO Survey for Emission-Line Galaxies. The final list resulted from follow-up spectroscopy conducted with the 4.5 m MMT telescope in 1996, and with 2.2 m CAHA and 6 m SAO telescopes in 2000 to 2003. The data of this snap-shot spectroscopy survey confirmed 134 emission-line objects out of 182 observed candidates and allowed their quantitative spectral classification and redshift determination. We classify 73 emission-line objects as definite or probable blue compact or Hii galaxies (BCG), 8 as QSOs, 4 as Seyfert 1 and 2 galaxies. 30 low-excitation objects were classified as definite or probable starburst nuclei (SBN), 3 as dwarf amorphous nuclei starburst galaxies (DANS) and 2 as LINERs. Due to the low signal-to-noise ratio we could not classify 14 ELGs (NON). For another 9 galaxies we did not detect any significant emission lines. For 98 emission-line galaxies, the redshifts and/or line intensities are determined for the first time. For the remaining 28 previously-known ELGs we give either improved data the line intensities or some independent measurements. The detection rate of ELGs is ~70%. This paper completes the classification of strong-lined ELGs found in the zone of the Hamburg/SAO survey. Together with previously known BCG/ galaxies in this zone, this sample of ~500 objects is the largest to date in a well bound region.

HS 2134+0400—a new very metal-poor galaxy, a representative of the void population?

We present the 6-m SAO telescope spectroscopy of HS 2134+0400, a blue compact galaxy (BCG) discovered within the framework of a dedicated Hamburg/SAO survey for low-metallicity BCGs (HSS-LM). Its very low abundance of oxygen (12 + log(O/H) = 7.44) and other heavy elements (S, N, Ne, Ar) allows this dwarf galaxy to be assigned to the group of eight lowest-metallicity BCGs among the several thousand BCGs known in the nearby Universe. The measured heavy-element abundance ratios (S/O, Ne/O, N/O, and Ar/O) are in good agreement with the typical values found for other very metal-poor BCGs. The spatial location of HS 2134+0400 is atypical of the majority of BCGs: it lies in the Pegasus void, a large region with a very low density of galaxies with normal or higher luminosities. In addition to HS 2134+0400, we found a dozen more very metal-poor galaxies in voids. Therefore, we discuss the hypothesis that this type of objects may be representative for the population of dwarf galaxies in voids.

On the nature of nearby GRB/SN host galaxies

We present and discuss optical diagnostics of the low redshift ( z < 0.2) galaxies that are known to have hosted supernovae associated with γ-ray bursts (GRBs). The three galaxies are all actively star forming sub-luminous ( L < L ⋆) galaxies with relatively low metallicities ( Z ≲ Z ⊙). We find no evidence for substantial internal extinction within any of the galaxies. We derive star formation rates (SFR) based on Hα luminosities, as well as specific star formation rates (SSFR, star formation rate per unit luminosity). For GRB 980425 (SN 1998bw) we use photometry of the supernova environment to estimate the mass of the progentitor to ≳30 M ⊙. These three host galaxies have global properties (luminosities, SFR, SSFR, metallicity, colour, reddening) that resemble those of more distant GRB host galaxies. We also compare the host galaxies with a sample of Blue Compact Galaxies (BCGs) in the local universe, and show that these samples have similar properties.

Spectroscopic study of blue compact galaxies

This is the fifth paper in a series studying the stellar components, star formation histories, star formation rates and metallicities of a blue compact galaxy (BCG) sample. Based on our high-quality ground-based spectroscopic observations, we have determined the electron temperatures, electron densities, nitrogen abundances and oxygen abundances for 72 star-forming BCGs in our sample, using different oxygen abundance indicators. The oxygen abundance covers the range , and nitrogen is found to be mostly a product of secondary nucleosynthesis for and apparently a product of primary nucleosynthesis for . To assess the possible systematic differences among different oxygen abundance indicators, we have compared oxygen abundances of BCGs obtained with the Te method, R23 method, P method, N2 method and O3N2 method. The oxygen abundances derived from the Te method are systematically lower by 0.1-0.25 dex than those derived from the strong line empirical abundance indicators, consistent with previous studies based on region samples. We confirm the existence of the metallicity-luminosity relation in BCGs over a large range of abundances and luminosities. Our sample of galaxies shows that the slope of the metallicity-luminosity relation for the luminous galaxies (~-0.05) is slightly shallower than that for the dwarf galaxies (~-0.17). An offset was found in the metallicity-luminosity relation of the local galaxies and that of the intermediate redshift galaxies. It shows that the metallicity-luminosity relation for the emission line galaxies at high redshift is displaced to lower abundances, higher luminosities, or both.

The [Feiv] Discrepancy: Constraining the Iron Abundances in Nebulae

We study the current discrepancy between the model-predicted and measured concentrations of Fe++ and Fe3+ in ionized nebulae. We calculate a set of photoionization models, updated with the atomic data relevant to the problem, and compare their results with those derived for the available nebulae where both [Fe III] and [Fe IV] lines have been measured. Our new model results are closer to the measured values than the results of previous calculations, but a discrepancy remains. This discrepancy translates into an uncertainty in the derived Fe abundances of a factor up to ~4. We explore the possible causes of this discrepancy and find that errors in the Fe atomic data may be the most likely explanation. The discrepancy can be fully accounted for by any of the following changes: (1) an increase by a factor of ~10 in the recombination rate (radiative plus dielectronic, or charge transfer) for Fe3+, (2) an increase by a factor of 2-3 in the effective collision strengths for Fe++, or (3) a decrease by a factor of 2-3 in the effective collision strengths for Fe3+. We derive the Fe abundances implied by these three explanations and use the results to constrain the degree of depletion of Fe in our sample nebulae. The Galactic H II regions and planetary nebulae are found to have high depletion factors, with less than 5% of their Fe atoms in the gas phase. The extragalactic H II regions (LMC 30 Doradus, SMC N88A, and SBS 0335-052) have somewhat lower depletions. The metal-deficient blue compact galaxy SBS 0335-052 could have from 13% to 40% of Fe in the gas phase. The depletions derived for the different objects define a trend of increasing depletion at higher metallicities.

The Nature of Nearby Counterparts to Intermediate‐Redshift Luminous Compact Blue Galaxies. II. CO Observations

We present the results of a single-dish beam-matched survey of the three lowest rotational transitions of CO in a sample of 20 local (D ≲ 70 Mpc) luminous compact blue galaxies (LCBGs). These ~L*, blue, high surface brightness, starbursting galaxies were selected on the same criteria used to define LCBGs at higher redshifts. Our detection rate was 70%, with those galaxies having LB < 7 × 109 L☉ not detected. We find that the H2 masses of local LCBGs range from 6.6 × 106 to 2.7 × 109 M☉, assuming a Galactic CO-to-H2 conversion factor. Combining these results with our earlier H I survey of the same sample, we find that the ratio of molecular to atomic gas mass is low, typically 5%-10%. Using a large velocity gradient model, we find that the average gas conditions of the entire interstellar medium in local LCBGs are similar to those found in the centers of star-forming regions in our Galaxy and in the nuclear regions of other galaxies. Star formation rates, determined from IRAS fluxes, are a few M☉ yr-1, much higher per unit dynamical mass than normal spiral galaxies. If this rate remains constant, the molecular hydrogen depletion timescales are short, ~10-200 Myr.