Blue Compact Galaxies Research Articles

A Complete 16 μm Selected Galaxy Sample at z ∼ 1. II. Morphological Analysis

We present a morphological analysis of the 16 μm flux-density-limited galaxy sample at 0.8 < z < 1.3 from Huang et al. (2021). At the targeted redshift, the 16 μm emission corresponds to the polycyclic aromatic hydrocarbon feature from intense star formation, or dust heated by active galactic nuclei (AGN). Our sample of 479 galaxies are dominated by luminous infrared galaxies (LIRGs; 67%) in three CANDLES fields (Extended Groth Strip, ​​​​Great Observatories Origins Deep Survey North and South fields), and are further divided into AGN-dominated, star-forming dominated, composite, and blue compact galaxies by their spectral energy distribution types. The majority of our sample (71%) have disk morphologies, with the few AGN-dominated galaxies being more bulge-dominated than the star-forming-dominated and composite galaxies. The distribution of our sample on the Gini versus M 20 plane is consistent with previous studies, where the Sérsic index n shows an increasing trend toward the smaller M 20 and higher Gini region below the dividing line for mergers. The subsample of ultraluminous infrared galaxies (ULIRGs) follows a steep size–mass relation that is closer to the early-type galaxies. In addition, as the 4.5 μm luminosity excess ( L4.5exc , proxy for AGN strength) increases, our sample appears to be more bulge dominated (i.e., higher n). Based on the specific star formation rate and compactness ( log10Σ1.5,Σ1.5=M*/Re1.5 ) diagram, the majority of our LIRG-dominated galaxy sample follows a secular evolution track, and their distribution can be explained without involving any merging activities. Out of the 16 ULIRGs in our sample, six are compact with strong AGN contributions, likely evolving along the fast track from more violent activities.

The influence of ionized gas kinematics on H ii galaxies – the cases of Tol 1004-296 and Tol 0957-278

ABSTRACT Blue compact galaxies, also known as H ii galaxies, are dwarf, star-forming objects with relatively simple dynamics, which allows for the investigation of star formation mechanisms in a cleaner manner compared to late-type objects. In this study, we have examined various characteristics of the interstellar medium, in connection with the kinematics and dynamics of ionized gas, in Tol 1004-296 and Tol 0957-278. These two objects were observed using the SOAR Integral Field Spectrometer (SIFS) attached to the Southern Observatory for Astrophysical Research (SOAR). Both galaxies were observed with two gratings: one with medium resolution for monochromatic and abundance maps, and another with high resolution for kinematics and profile analysis. Additionally, we conducted an analysis on the velocity and velocity dispersion maps using intensity–velocity dispersion (I-σ) and velocity–velocity dispersion (Vr-σ) diagrams. Neither object exhibits a rotation pattern, and only Tol 1004-296 shows a velocity gradient between the two principal knots. However, the study reveals the significant role played by velocity dispersion in the star formation process. Specifically, we identified a relationship between monochromatic intensity, metallicity, and velocity dispersion, where high emission corresponds to low metallicity and low velocity dispersion. Tol 1004-296, in particular, exhibits a distinctive linear high velocity dispersion pattern between the two main knots, suggesting that both star formation sites are pushing the gas in opposite directions.

A ∼15 kpc outflow cone piercing through the halo of the blue compact metal-poor galaxy SBS 0335–052E

Context. Outflows from low-mass star-forming galaxies are a fundamental ingredient for models of galaxy evolution and cosmology. Despite seemingly favourable conditions for outflow formation in compact starbursting galaxies, convincing observational evidence for kiloparsec-scale outflows in such systems is scarce. Aims. The onset of kiloparsec-scale ionised filaments in the halo of the metal-poor compact dwarf SBS 0335−052E was previously not linked to an outflow. In this paper we investigate whether these filaments provide evidence for an outflow. Methods. We obtained new VLT/MUSE WFM and deep NRAO/VLA B-configuration 21 cm data of the galaxy. The MUSE data provide morphology, kinematics, and emission line ratios of Hβ/Hα and [O III]λ5007/Hα of the low surface-brightness filaments, while the VLA data deliver morphology and kinematics of the neutral gas in and around the system. Both datasets are used in concert for comparisons between the ionised and the neutral phase. Results. We report the prolongation of a lacy filamentary ionised structure up to a projected distance of 16 kpc at SBHα = 1.5 × 10−18 erg s cm−2 arcsec−2. The filaments exhibit unusual low Hα/Hβ ≈ 2.4 and low [O III]/Hα ∼ 0.4 − 0.6 typical of diffuse ionised gas. They are spectrally narrow (∼20 km s−1) and exhibit no velocity sub-structure. The filaments extend outwards from the elongated H I halo. On small scales, the NHI peak is offset from the main star-forming sites. The morphology and kinematics of H I and H II reveal how star-formation-driven feedback interacts differently with the ionised and the neutral phase. Conclusions. We reason that the filaments are a large-scale manifestation of star-formation- driven feedback, namely limb-brightened edges of a giant outflow cone that protrudes through the halo of this gas-rich system. A simple toy model of such a conical structure is found to be commensurable with the observations.

Warm ionized gas in the blue compact galaxy Haro 14 viewed by MUSE

We investigate the warm ionized gas in the blue compact galaxy (BCG) Haro 14 by means of integral field spectroscopic observations taken with the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope. The large field of view of MUSE and its unprecedented sensitivity enable observations of the galaxy nebular emission up to large galactocentric distances, even in the important but very faint [O I] λ6300 diagnostic line. This allowed us to trace the ionized gas morphology and ionization structure of Haro 14 up to kiloparsec scales and, for the first time, to accurately investigate the excitation mechanism operating in the outskirts of a typical BCG. The intensity and diagnostic maps reveal at least two highly distinct components of ionized gas: the bright central regions, mostly made of individual clumps, and a faint component which extends up to kiloparsec scales and consists of widespread diffuse emission, well-delineated filamentary structures, and faint knots. Noteworthy are the two curvilinear filaments extending up to 2 and 2.3 kpc southwest, which likely trace the edges of supergiant expanding bubbles driven by galactic outflows. We find that while the central clumps in Haro 14 are H II-region complexes, the morphology and line ratios of the whole low-surface-brightness component are not compatible with star formation photoionization. In the spatially resolved emission-line-ratio diagnostic diagrams, spaxels above the maximum starburst line form the majority (∼75% and ∼50% in the diagnostic diagrams involving [O I] and [S II] respectively). Moreover, our findings suggest that more than one alternative mechanism is ionizing the outer galaxy regions. The properties of the diffuse component are consistent with ionization by diluted radiation and the large filaments and shells are most probably shocked areas at the edge of bubbles. The mechanism responsible for the ionization of the faint individual clumps observed in the galaxy periphery is more difficult to assess. These clumps could be the shocked debris of fragmented shells or regions where star formation is proceeding under extreme conditions.

MUSE observations of the blue compact dwarf galaxy Haro 14

Investigations of blue compact galaxies (BCGs) are essential to advancing our understanding of galaxy formation and evolution. BCGs are low-luminosity, low-metallicity, gas-rich objects that form stars at extremely high rates, meaning they are good analogs to the high-redshift star-forming galaxy population. Being low-mass starburst systems, they also constitute excellent laboratories in which to investigate the star formation process and the interplay between massive stars and their surroundings. This work presents results from integral field spectroscopic observations of the BCG Haro 14 taken with the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope in wide-field adaptive optics mode. The large MUSE field of view (1′×1′ = 3.8 × 3.8 kpc2 at the adopted distance of 13 Mpc) enables simultaneous observations of the central starburst and the low-surface-brightness host galaxy, which is a huge improvement with respect to previous integral field spectroscopy of BCGs. From these data we built galaxy maps in continuum and in the brightest emission lines. We also generated synthetic broad-band images in the VRI bands, from which we produced color index maps and surface brightness profiles. We detected numerous clumps spread throughout the galaxy, both in continuum and in emission lines, and produced a catalog with their position, size, and photometry. This analysis allowed us to study the morphology and stellar populations of Haro 14 in detail. The stellar distribution shows a pronounced asymmetry; the intensity peak in continuum is not centered with respect to the underlying stellar host but is displaced by about 500 pc southwest. At the position of the continuum peak we find a bright stellar cluster that with Mv = −12.18 appears as a strong super stellar cluster candidate. We also find a highly asymmetric, blue, but nonionizing stellar component that occupies almost the whole eastern part of the galaxy. We conclude that there are at least three different stellar populations in Haro 14: the current starburst of about 6 Myr; an intermediate-age component of between ten and several hundred million years; and a red and regular host of several gigayears. The pronounced lopsidedness in the continuum and also in the color maps, and the presence of numerous stellar clusters, are consistent with a scenario of mergers or interactions acting in Haro 14.

Ionization correction factors and dust depletion patterns in giant H ii regions

ABSTRACT We provide new ionization correction factors (ICFs) for carbon, nitrogen, neon, sulfur, chlorine, and argon in giant H ii regions. The ICFs were computed using the most representative photoionization models from a large initial grid. The models were selected using an observational sample of 985 giant H ii regions (GHR) in spiral galaxies and blue compact galaxies (BCG). The observational sample was also used to assign a weight to each model describing how well it agrees with observations in the [O iii]/H β versus [N ii]/H α diagram. In addition to the ICFs we provide, for the first time, analytical expressions for their formal uncertainties. We use our ICFs to compute the abundances of nitrogen, neon, sulfur, and argon in our samples. Our abundances are robust within the adopted framework, but may require revision in the case of important changes in atomic data or in the spectral energy distribution of the ionizing radiation in H ii regions. Considering the abundance patterns we obtained for the BCG sample (abundances for the GHR sample are less reliable) we find that oxygen is depleted into dust grains at a rate increasing with metallicity and reaching 0.12 dex at solar abundances. The discussion of possible depletion of sulfur and argon requires considering recent Type Ia Supernova yields, which are still uncertain.

The Source of Leaking Ionizing Photons from Haro11: Clues from HST/COS Spectroscopy of Knots A, B, and C*

Abstract Understanding the escape of ionizing (Lyman continuum) photons from galaxies is vital for determining how galaxies contributed to reionization in the early universe. While directly detecting the Lyman continuum from high-redshift galaxies is impossible due to the intergalactic medium, low-redshift galaxies in principle offer this possibility but require observations from space. The first local galaxy for which Lyman continuum escape was found is Haro 11, a luminous blue compact galaxy at z = 0.02, where observations with the FUSE satellite revealed an escape fraction of 3.3%. However, the FUSE aperture covers the entire galaxy, and it is not clear from where the Lyman continuum is leaking out. Here we utilize Hubble Space Telescope/Cosmic Origins Spectrograph spectroscopy in the wavelength range 1100–1700 Å of the three knots (A, B, and C) of Haro 11 to study the presence of Lyα emission and the properties of intervening gas. We find that all knots have bright Lyα emission. UV absorption lines, originating in the neutral interstellar medium, as well as lines probing the ionized medium, are seen extending to blueshifted velocities of 500 km s−1 in all three knots, demonstrating the presence of an outflowing multiphase medium. We find that knots A and B have large covering fractions of neutral gas, making LyC escape along these sightlines improbable, while knot C has a much lower covering fraction (≲50%). Knot C also has the the highest Lyα escape fraction, and we conclude that it is the most likely source of the escaping Lyman continuum detected in Haro 11.

The Evolution of the Luminosity Function for Luminous Compact Blue Galaxies to z = 1

Abstract Luminous compact blue galaxies (LCBGs) are compact, star-forming galaxies that are rarely observed in the local universe but abundant at z = 1. This increase in LCBG number density over cosmic lookback time roughly follows the increase in the star formation rate density of the universe over the same period. We use publicly available data in the COSMOS field to study the evolution of the largest homogeneous sample of LCBGs to date by deriving their luminosity function in four redshift bins over the range 0.1 ≤ z ≤ 1. We find that over this redshift range, the characteristic luminosity (M*) increases by ∼0.2 mag, and the number density increases by a factor of 4. While LCBGs make up only about 18% of galaxies more luminous than M B = −18.5 at z ∼ 0.2, they constitute roughly 54% at z ∼ 0.9. The strong evolution in number density indicates that LCBGs are an important population of galaxies to study in order to better understand the decrease in the star formation rate density of the universe since z ∼ 1.

Massive Star Formation in the Ultraviolet Observed with the Hubble Space Telescope

Spectroscopic observations of a massive star formation in the ultraviolet and their interpretation are reviewed. After a brief historical retrospective, two well-studied resolved star clusters and the surrounding H II regions are introduced: NGC 2070 in the Large Magellanic Cloud and NGC 604 in M33. These regions serve as a training set for studies of more distant clusters, which can no longer be resolved into individual stars. Observations of recently formed star clusters and extended regions in star-forming galaxies in the nearby universe beyond the Local Group are presented. Their interpretation relies on spectral synthesis models. The successes and failures of such models are discussed, and future directions are highlighted. I present a case study of the extraordinary star cluster and giant H II region in the blue compact galaxy II Zw 40. The review concludes with a preview of two upcoming Hubble Space Telescope programs: ULLYSES, a survey of massive stars in nearby galaxies, and CLASSY, a study of massive star clusters in star-forming galaxies.

Understanding star formation and feedback in small galaxies

Context. Low-luminosity, active star-forming blue compact galaxies (BCGs) are excellent laboratories for investigating the process of star formation on galactic scales and to probe the interplay between massive stars and the surrounding interstellar (or intergalactic) medium. Aims. We investigate the morphology, structure, and stellar content of BCG Mrk 900, as well as the excitation, ionization conditions, and kinematics of its H II regions and surrounding ionized gas. Methods. We obtained integral field observations of Mrk 900 working with the Visible Multi-Object Spectrograph at the Very Large Telescope. The observations were taken in the wavelength range 4150−7400 Å covering a field of view of 27″ × 27″ on the sky with a spatial sampling of 0.″67. From the integral field data we built continuum, emission, and diagnostic line ratio maps and produced velocity and velocity dispersion maps. We also generated the integrated spectrum of the major H II regions and the nuclear area to determine reliable physical parameters and oxygen abundances. Integral field spectroscopy was complemented with deep broad-band photometry taken at the 2.5 m NOT telescope; the broad-band data, tracing the galaxy up to radius 4 kpc, allowed us to investigate the properties of the low surface brightness underlying stellar host. Results. We disentangle two different stellar components in Mrk 900: a young population, which resolves into individual stellar clusters with ages ∼5.5−6.6 Myr and extends about 1 kpc along the galaxy minor axis, is placed on top of a rather red and regular shaped underlying stellar host, several Gyr old. We find evidence of a substantial amount of dust and an inhomogeneous extinction pattern, with a dust lane crossing the central starburst. Mrk 900 displays overall rotation, although distorted in the central, starburst regions; the dispersion velocity map is highly inhomogeneous, with values increasing up to 60 km s−1 at the periphery of the SF regions, where we also find hints of the presence of shocks. Our observational results point to an interaction or merger with a low-mass object or infalling gas as plausible trigger mechanisms for the present starburst event.

The interstellar medium of dwarf galaxies: new insights from Machine Learning analysis of emission-line spectra

Dwarf galaxies are ideal laboratories to study the physics of the interstellar medium (ISM). Emission lines have been widely used to this aim. Retrieving the full information encoded in the spectra is therefore essential. This can be efficiently and reliably done using Machine Learning (ML) algorithms. Here, we apply the ML code GAME to MUSE (Multi Unit Spectroscopic Explorer) and PMAS (Potsdam Multi Aperture Spectrophotometer) Integral Field Unit (IFU) observations of two nearby Blue Compact Galaxies (BCGs): Henize 2-10 and IZw18. We derive spatially resolved maps of several key ISM physical properties. We find that both galaxies show a remarkably uniform metallicity distribution. Henize 2-10 is a star forming dominated galaxy, with a Star Formation Rate (SFR) of about 1.2 M$_{\odot}$ yr$^{-1}$. Henize 2-10 features dense and dusty ($A_V$ up to 5-7 mag) star forming central sites. We find IZw18 to be very metal-poor ($Z$= 1/20 $Z_{\odot}$). IZw18 has a strong interstellar radiation field, with a large ionization parameter. We also use models of PopIII stars spectral energy distribution as a possible ionizing source for the HeII $\lambda$4686 emission detected in the IZw18 NW component. We find that PopIII stars could provide a significant contribution to the line intensity. The upper limit to the PopIII star formation is 52% of the total IZw18 SFR.

The Role of Black Hole Feedback on Size and Structural Evolution in Massive Galaxies

Abstract We use cosmological hydrodynamical simulations to investigate the role of feedback from accreting black holes in the evolution of the size, compactness, stellar core density, and specific star formation of massive galaxies with stellar masses of . We perform two sets of cosmological zoom-in simulations of 30 halos to z = 0: (1) without black holes and active galactic nucleus (AGN) feedback and (2) with AGN feedback arising from winds and X-ray radiation. We find that AGN feedback can alter the stellar density distribution, reduce the core density within the central 1 kpc by 0.3 dex from z = 1, and enhance the size growth of massive galaxies. We also find that galaxies simulated with AGN feedback evolve along tracks similar to those characterized by observations of specific star formation rate versus compactness. We confirm that AGN feedback plays an important role in transforming galaxies from blue compact galaxies into red extended galaxies in two ways: (1) it effectively quenches the star formation, transforming blue compact galaxies into compact quiescent galaxies, and (2) it also removes and prevents new accretion of cold gas, shutting down in situ star formation and causing subsequent mergers to be gas-poor or mixed. Gas-poor minor mergers then build up an extended stellar envelope. AGN feedback also puffs up the central region through fast AGN-driven winds as well as the slow expulsion of gas while the black hole is quiescent. Without AGN feedback, large amounts of gas accumulate in the central region, triggering star formation and leading to overly massive blue galaxies with dense stellar cores.

The Lyman Alpha Reference Sample

Context. The Lyman α Reference Sample (LARS) of 14 star-forming galaxies offers a wealth of insight into the workings of these local analogs to high-redshift star-forming galaxies. The sample has been well-studied in terms of Lyα and other emission line properties, such as H I mass, gas kinematics, and morphology. Aims. We analyze deep surface photometry of the LARS sample in UBIK broadband imaging obtained at the Nordic Optical Telescope and the Canada-France-Hawaii Telescope, and juxtaposition their derived properties with a sample of local high-redshift galaxy analogs, namely, with blue compact galaxies (BCGs). Methods. We construct radial surface brightness and color profiles with both elliptical and isophotal integration, as well as RGB images, deep contours, color maps, a burst fraction estimate, and a radial mass-to-light ratio profile for each LARS galaxy. Standard morphological parameters like asymmetry, clumpiness, the Gini and M20 coefficients are also obtained and analyzed, as well as isophotal asymmetry profiles for each galaxy. In this context, we compare the LARS sample to the properties of the BCG sample and highlight the differences. Results. Several of these diagnostics indicate that the LARS galaxies have highly disturbed morphologies even at the level of the faintest outer isophotes, with no hint at a regular underlying population, as found in many BCG sample galaxies. The ground-based photometry reaches isophotes down to ~28 mag arcsec−2, while the space-based data reach only ~26 mag arcsec−2. The ground-based observations therefore reveal previously unexplored isophotes of the LARS galaxies. The burst fraction estimate suggests a spatially more extended burst region in LARS than in the BCGs. Comparison to stellar evolutionary models in color–color diagrams reveals complex behavior of the radial color profiles, often inconsistent with a single stellar population of any age and metallicity, but instead suggesting a mixture of at least two stellar populations with a typical young mass fraction in the range 0.1–1%. Conclusions. The galaxies in the LARS sample appear to be in earlier stages of a merger event compared to the BCGs. Standard morphological diagnostics like asymmetry, clumpiness, Gini and M20 coefficients cannot separate the two samples, although an isophotal asymmetry profile successfully captures the average difference in morphology. These morphological diagnostics do not show any correlation with the equivalent width or the escape fraction of Lyman Alpha.

Resolved H i Observations of Local Analogs to z ∼ 1 Luminous Compact Blue Galaxies: Evidence for Rotation-supported Disks

Abstract While bright, blue, compact galaxies are common at , they are relatively rare in the local universe, and their evolutionary paths are uncertain. We have obtained resolved H i observations of nine luminous compact blue galaxies (LCBGs) using the Giant Metrewave Radio Telescope and Very Large Array in order to measure their kinematic and dynamical properties and better constrain their evolutionary possibilities. We find that the LCBGs in our sample are rotating galaxies that tend to have nearby companions, relatively high central velocity dispersions, and can have disturbed velocity fields. We calculate rotation velocities for each galaxy by measuring half of the velocity gradient along their major axes and correcting for inclination using axis ratios derived from SDSS images of each galaxy. We compare our measurements to those previously made with single dishes and find that single-dish measurements tend to overestimate LCBGs’ rotation velocities and H i masses. We also compare the ratio of LCBGs’ rotation velocities and velocity dispersions to those of other types of galaxies and find that LCBGs are strongly rotationally supported at large radii, similar to other disk galaxies, though within their half-light radii the values of their H i are comparable to stellar values of dwarf elliptical galaxies. We find that LCBGs’ disks on average are gravitationally stable, though conditions may be conducive to local gravitational instabilities at the largest radii. Such instabilities could lead to the formation of star-forming gas clumps in the disk, resulting eventually in a small central bulge or bar.

Probing star formation and feedback in dwarf galaxies

Context. Blue compact galaxies (BCG) are gas-rich, low-mass, small systems that form stars at unusually high rates. This makes them excellent laboratories for investigating the process of star-formation (SF) at galactic scales and the effects of massive stellar feedback on the interstellar (and intergalactic) medium.

Star-forming galaxies in intermediate-redshift clusters: stellar versus dynamical masses of luminous compact blue galaxies

We investigate the stellar masses of the class of star-forming objects known as Luminous Compact Blue Galaxies (LCBGs) by studying a sample of galaxies in the distant cluster MS$~$0451.6-0305 at $z\approx0.54$ with ground-based multicolor imaging and spectroscopy. For a sample of 16 spectroscopically-confirmed cluster LCBGs (colour $B-V < 0.5$, surface brightness $\mu_B < 21$ mag arcsec$^{-2}$, and magnitude $M_B < -18.5$), we measure stellar masses by fitting spectral energy distribution (SED) models to multiband photometry, and compare with dynamical masses (determined from velocity dispersion between 10 $<$ $\sigma_v (\rm km~ s^{-1})$ $<$ 80), we previously obtained from their emission-line spectra. We compare two different stellar population models that measure stellar mass in star-bursting galaxies, indicating correlations between the stellar age, extinction, and stellar mass derived from the two different SED models. The stellar masses of cluster LCBGs are distributed similarly to those of field LCBGs, but the cluster LCBGs show lower dynamical-to-stellar mass ratios ($\rm M_{dyn}/M_{\ast} = 2.6$) than their field LCBG counterparts ($\rm M_{dyn}/M_{\ast}=4.8$), echoing trends noted previously in low-redshift dwarf elliptical galaxies. Within this limited sample, the specific star formation rate declines steeply with increasing mass, suggesting that these cluster LCBGs have undergone vigorous star formation.

Integral field observations of the blue compact galaxy Haro14

(Abridged) Low-luminosity, gas-rich blue compact galaxies (BCG) are ideal laboratories to investigate many aspects of the star formation in galaxies. We study the morphology, stellar content, kinematics, and the nebular excitation and ionization mechanism in the BCG Haro 14 by means of integral field observations with VIMOS in the VLT. From these data we build maps in continuum and in the brighter emission lines, produce line-ratio maps, and obtain the velocity and velocity dispersion fields. We also generate the integrated spectrum of the major HII regions and young stellar clusters identified in the maps to determine reliable physical parameters and oxygen abundances. We find as follows: i) the current star formation in Haro 14 is spatially extended with the major HII regions placed along a linear structure, elongated in the north-south direction, and in a horseshoe-like curvilinear feature that extends about 760 pc eastward; the continuum emission is more concentrated and peaks close to the galaxy center; ii) two different episodes of star formation are present: the recent starburst, with ages $\leq$ 6 Myrs and the intermediate-age clusters, with ages between 10 and 30 Myrs; these stellar components rest on a several Gyr old underlying host galaxy; iii) the H$\alpha$/H$\beta$ pattern is inhomogeneous, with excess color values varying from E(B-V)=0.04 up to E(B-V)=1.09; iv) shocks play a significant role in the galaxy; and v) the velocity field displays a complicated pattern with regions of material moving toward us in the east and north galaxy areas. The morphology of Haro 14, its irregular velocity field, and the presence of shocks speak in favor of a scenario of triggered star formation. Ages of the knots are consistent with the ongoing burst being triggered by the collective action of stellar winds and supernovae originated in the central clusters.

DETECTION OF H i IN EMISSION IN THE LYα EMITTING GALAXY HARO 11

ABSTRACT We present the first robust detection of H i 21 cm emission in the blue compact galaxy Haro 11 using the 100 m Robert C. Byrd Green Bank Telescope (GBT). Haro 11 is a luminous blue compact galaxy with emission in both Lyα and the Lyman continuum. We detect (5.1 ± 0.7 × 108) M ⊙ of H i gas at an assumed distance of 88 Mpc, making this galaxy H i deficient compared to other local galaxies with similar optical properties. Given this small H i mass, Haro 11 has an elevated M H2/M H i ratio and a very low gas fraction compared to most local galaxies, and contains twice as much mass in ionized hydrogen as in neutral hydrogen. The H i emission has a linewidth of 71 km s−1 and is offset 60 km s−1 redward of the optical line center. It is undergoing a starburst after a recent merger that has elevated the star formation rate, and will deplete the gas supply in &lt;0.2 Gyr. Although this starburst has elevated the star formation rate (SFR) compared to galaxies with similar H i masses and line widths, Haro 11 matches a trend of lower gas fractions toward higher SFRs and is below the general trend of increasing H i mass with increasing luminosity. Taken together, our results paint Haro 11 as a standard low-mass galaxy that is undergoing an unusually efficient star formation episode.

SPECTROSCOPY OF LUMINOUS COMPACT BLUE GALAXIES IN DISTANT CLUSTERS. II. PHYSICAL PROPERTIES OF dE PROGENITOR CANDIDATES

ABSTRACT Luminous Compact Blue Galaxies (LCBGs) are an extreme star-bursting population of galaxies that were far more common at earlier epochs than today. Based on spectroscopic and photometric measurements of LCBGs in massive (M &gt; 1015 M ⊙), intermediate redshift (0.5 &lt; z &lt; 0.9) galaxy clusters, we present their rest-frame properties including star formation rate, dynamical mass, size, luminosity, and metallicity. The appearance of these small, compact galaxies in clusters at intermediate redshift helps explain the observed redshift evolution in the size–luminosity relationship among cluster galaxies. In addition, we find the rest-frame properties of LCBGs appearing in galaxy clusters are indistinguishable from field LCBGs at the same redshift. Up to 35% of the LCBGs show significant discrepancies between optical and infrared indicators of star formation, suggesting that star formation occurs in obscured regions. Nonetheless, the star formation for LCBGs shows a decrease toward the center of the galaxy clusters. Based on their position and velocity, we estimate that up to 10% of cluster LCBGs are likely to merge with another cluster galaxy. Finally, the observed properties and distributions of the LCBGs in these clusters lead us to conclude that we are witnessing the quenching of the progenitors of dwarf elliptical galaxies that dominate the number density of present-epoch galaxy clusters.

Kinematics of Haro 11: The miniature Antennae

(abridged) Luminous blue compact galaxies are among the most active galaxies in the local universe in terms of their star formation rate per unit mass. They may be seen as the local analogs of higher redshift Lyman Break Galaxies. Studies of their kinematics is key to understanding what triggers their unusually active star formation In this work we investigate the kinematics of stars and ionised gas in Haro11, one of the most luminous blue compact galaxies in the local universe. Previous works have indicated that many such galaxies may be triggered by galaxy mergers. We have employed Fabry-Perot interferometry, long-slit spectroscopy and Integral Field Unit (IFU) spectroscopy to explore the kinematics of Haro11. We target the near infrared Calcium triplet to derive the stellar velocity field and velocity dispersion. Ionised gas is analysed through emission lines from hydrogen, [OIII] , and [SIII]. When spectral resolution and signal to noise allows we investigate the the line profile in detail and identify multiple velocity components when present. We find that to first order, the velocity field and velocity dispersions derived from stars and ionised gas agree. Hence the complexities reveal real dynamical disturbances providing further evidence for a merger in Haro11. Through decomposition of emission lines we find evidence for kinematically distinct components, for instance a tidal arm behind the galaxy. The ionised gas velocity field can be traced to large galactocentric radii, and shows significant velocity dispersion even far out in the halo. We discuss the origin of the line width, and interpreted as virial motions it indicates a mass of ~1E11 M_sun. Morphologically and kinematically Haro11 shows many resemblances with the famous Antennae galaxies, but is much denser which is the likely explanation for the higher star formation efficiency in Haro11.