The morphology of H II galaxies (original) (raw)
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Narrow-band Hβ images of star-formation regions in HII galaxies
Astronomy & Astrophysics, 2007
Aims. Create a catalog of images of HII galaxies and their individual star-formation regions in order to study the distribution of the gas emission and their underlying stellar continuum. Methods. We have used Hβ narrow-band images of 43 selected HII galaxies obtained at ESO NTT 3.58 m telescope using the SUSI2 camera. Results. Surface photometric Hβ fluxes and equivalent widths for all objects and star-formation regions are presented in this catalog. A myriad of filamentary structure were found in the pure Hβ emission-line or continuum-subtracted images, probably attributed to expanding shells as a consequence of the star-formation activity. Our results indicate that the number of regions with high Hβ equivalent width or young regions increase with the instrumental resolution, showing that the instrumental resolution is a bias to determine the cluster ages. Therefore, we showed that some of the observed giant HII regions may have been formed by ensembles of unresolved star forming regions or candidates to host Super Star Clusters. Pure Hβ emission-line images, continuum contours and EW(Hβ) maps showing the morphology of the gaseous and stellar emission in HII galaxies and their individual star-formation regions were obtained. All calibrated continuum and Hβ emission line fluxes and the derived Hβ equivalent width images are available in fits format from http://www.on.br/astro/etelles/HIIgalaxies/Hbeta/.
The Astronomical Journal, 2004
We performed Hα imaging observations of 22 luminous infrared galaxies to investigate how the distribution of star-forming regions in these galaxies is related to galaxy interactions. Based on correlation diagrams between Hα flux and continuum emission for individual galaxies, a sequence for the distribution of star-forming regions was found: very compact (∼ 100 pc) nuclear starbursts with almost no star-forming activity in the outer regions (type 1), dominant nuclear starbursts 1 kpc in size and a negligible contribution from the outer regions (type 2), nuclear starbursts 1 kpc in size and a significant contribution from the outer regions (type 3), and extended starbursts with relatively faint nuclei (type 4). These classes of star-forming region were found to be strongly related to global star-forming properties such as star-formation efficiency, farinfrared color, and dust extinction. There was a clear tendency for the objects with more compact distributions of star-forming regions to show a higher star-formation efficiency and hotter far-infrared color. An appreciable fraction of the sample objects were dominated by extended starbursts (type 4), which is unexpected in the standard scenario of interaction-induced starburst galaxies. We also found that the distribution of star-forming regions was weakly but clearly related to galaxy morphology: severely disturbed objects had a more concentrated distribution of star-forming regions. This suggests that the properties of galaxy interactions, such as dynamical phase and orbital 1 Visiting Astronomer, Okayama Astrophysical Observatory of National Astronomical Observatory.
STAR FORMATION IN H i–SELECTED GALAXIES. II. H ii REGION PROPERTIES
A sample of 69 galaxies with radial velocities less than 2500 km s À1 was selected from the H i Parkes All Sky Survey (HiPASS) to deduce details about star formation in nearby disk galaxies selected with no bias to optical surface brightness selection effects. Broadband (B and R) and narrowband (H) images were obtained for all of these objects. More than half of the sample galaxies are late-type, dwarf disks (mostly Sc and Sm galaxies). We have measured the properties of the H ii regions on H continuum–subtracted images, using the HIIphot package developed by Thilker et al. All but one of the galaxies contained at least one detectable H ii region. Examination of the properties of the H ii regions in each galaxy revealed that the brightest regions in higher surface brightness galaxies tend to be more luminous than those in lower surface brightness galaxies. A higher fraction (referred to as the diffuse fraction) of the H emission from lower surface brightness galaxies comes from diffuse ionized gas. H ii region luminosity functions (LFs) co-added according to surface brightness show that the shapes of the LFs for the lowest surface brightness galaxies are different from those for typical spiral galaxies. This discrepancy could be caused by the lowest surface brightness galaxies having somewhat episodic star formation or by them forming a relatively larger fraction of their stars outside of dense, massive molecular clouds. In general, the results imply that the conditions under which star formation occurs in lower surface brightness galaxies are different than in more typical, higher surface brightness spiral galaxies.
Narrow-band {H}beta images of star-formation regions in HII galaxies
Astronomy & Astrophysics, 2007
Aims:Create a catalog of images of HII galaxies and their individual star-formation regions in order to study the distribution of the gas emission and their underlying stellar continuum. Methods: We have used Hβ narrow-band images of 43 selected HII galaxies obtained at ESO NTT 3.58 m telescope using the SUSI2 camera. Results: Surface photometric Hβ fluxes and equivalent widths for all objects and star-formation regions are presented in this catalog. A myriad of filamentary structure were found in the pure Hβ emission-line or continuum-subtracted images, probably attributed to expanding shells as a consequence of the star-formation activity. Our results indicate that the number of regions with high Hβ equivalent width or young regions increase with the instrumental resolution, showing that the instrumental resolution is a bias to determine the cluster ages. Therefore, we showed that some of the observed giant HII regions may have been formed by ensembles of unresolved star forming regions or candidates to host Super Star Clusters. Pure Hβ emission-line images, continuum contours and EW(Hβ) maps showing the morphology of the gaseous and stellar emission in HII galaxies and their individual star-formation regions were obtained. All calibrated continuum and Hβ emission line fluxes and the derived Hβ equivalent width images are available in fits format from http://www.on.br/astro/etelles/HIIgalaxies/Hbeta/. Based on observations made with ESO NTT 3.5 m Telescope at the La Silla Observatory under programmen ID < 68.B-0678(A) > and < 70.B-0184(A) >. Tables [see full textsee full textsee full textsee full text], [see full textsee full textsee full textsee full text] and Figs. [see full textsee full textsee full textsee full text], [see full textsee full textsee full textsee full text] are only available in electronic form at http://www.aanda.org
Quantified HI Morphology I: Multi-Wavelengths Analysis of the THINGS Galaxies
Galaxy evolution is driven to a large extent by interactions and mergers with other galaxies and the gas in galaxies is extremely sensitive to the interactions. One method to measure such interactions uses the quantified morphology of galaxy images. Well-established parameters are Concentration, Asymmetry, Smoothness, Gini, and M20 of a galaxy image. Thus far, the application of this technique has mostly been restricted to restframe ultra-violet and optical images. However, with the new radio observatories being commissioned (MeerKAT, ASKAP, EVLA, WSRT/APERTIF, and ultimately SKA), a new window on the neutral atomic hydrogen gas (HI) morphology of a large numbers of galaxies will open up. The quantified morphology of gas disks of spirals can be an alternative indicator of the level and frequency of interaction. The HI in galaxies is typically spatially more extended and more sensitive to low-mass or weak interactions. In this paper, we explore six morphological parameters calculated...
Star Formation Properties of a Large Sample of Irregular Galaxies
The Astronomical Journal, 2004
We present the results of Hα imaging of a large sample of irregular galaxies. Our sample includes 94 galaxies with morphological classifications of Im, 26 Blue Compact Dwarfs (BCDs), and 20 Sm systems. The sample spans a large range in galactic parameters including integrated absolute magnitude (M V of −9 to −19), average surface brightness (20 to 27 mag/arcsec 2), current star formation activity (0 to 1.3 M ⊙ yr −1 kpc −2), and relative gas content (0.02 to 5 M ⊙ /L B). The Hα images were used to measure the integrated star formation rates, determine the extents of star formation in the disks, and compare azimuthallyaveraged radial profiles of current star formation to older starlight. The integrated star formation rates of Im galaxies normalized to the physical size of the galaxy span a range of a factor of 10 4 with 10% Im galaxies and one Sm system having no measureable star formation at the present time. The BCDs fall, on average, at the high star formation rate end of the range. We find no correlation between star formation activity and proximity to other catalogued galaxies. Two galaxies located in voids are similar in properties to the Sm group in our sample. The H ii regions in these galaxies are most often found within the Holmberg radius R H , although in a few systems H ii regions are traced as far as 1.7R H. Similarly, most of the star formation is found within 3 disk scale-lengths R D , but in some galaxies H ii regions are traced as far as 6R D. A comparison of Hα surface photometry with V-band surface photometry shows that the two approximately follow each other with radius in Sm galaxies, but in most BCDs there is an excess of Hα emission in the centers that drops
HST imaging of CFRS and LDSS galaxies-I: Morphological Properties
Arxiv preprint astro-ph/ …, 1997
We analyse Hubble Space Telescope images of a complete sample of 341 galaxies drawn from both the Canada France and Autofib/Low Dispersion Survey Spectrograph ground-based redshift surveys. In this, the first paper in the series, each galaxy has been morphologically classified according to a scheme similar to that developed for the Medium Deep Survey. We discuss the reproducibility of these classifications and quantify possible biases that may arise from various redshift-dependent effects. We then discuss automated classifications of the sample and conclude, from several tests, that we can expect an apparent migration with redshift to later Hubble types that corresponds to a misclassification in our adopted machine classification system of ∼ 24% ± 11 of the true "spirals" as "peculiars" at a redshift z ≃0.9. After allowing for such biases, the redshift distribution for normal spirals, together with their luminosity function derived as a function of redshift, indicates approximately 1 magnitude of luminosity evolution in B AB by z ≃ 1. The elliptical sample is too small for precise evolutionary constraints. However, we find a substantial increase in the proportion of galaxies with irregular morphology at large redshift from 9% ± 3% for 0.3 ≤ z ≤ 0.5 to 32% ± 12% for 0.7 ≤ z ≤ 0.9. These galaxies also appear to be the dominant cause of the rapid rise with redshift in the blue luminosity density identified in the redshift surveys. Although galaxies with irregular morphology may well comprise a mixture of
A Comparative Study of Star-forming and Quiescent Dwarf Galaxies
Astronomical Journal, 2000
We present the results from a comparative study of the atomic hydrogen (H I) and optical properties of a sample of 16 dwarf galaxies, chosen to investigate the e †ects of star formation on the properties of low-mass systems. The violent star formation bursts believed to occur in these low-mass systems suggest a possible connection between the actively star-forming blue compact dwarfs (BCDs), and the quiescent low surface brightness dwarfs (LSBDs). It has been suggested that LSBDs, upon undergoing a burst of star formation, will evolve into BCDs and then back into LSBDs when the star formation slows or stops as the H I column density falls below the critical threshold necessary to support it. We have examined the location and kinematics of H I in eight BCDs and eight LSBDs of similar H I masses and a range of color indices to investigate this "" evolutionary ÏÏ sequence. The starburst episodes in these low-mass galaxies should lead to (1) a dispersal/depletion of the H I seen in the eight LSB dwarfs and (2) more centrally concentrated and agitated H I in the eight BCDs. The results of this project indicate that the quiescent LSBD galaxies have more di †use H I distributions and often show a ringlike structure, while the active galaxies have more highly centrally concentrated H I reservoirs. The bluer, more recently active systems of both types also have higher internal H I velocity dispersions, indicating that energy has been pumped into the interstellar medium of these galaxies. These observations are consistent with an evolutionary scheme wherein the H I reservoirs in these galaxies take on di †erent characteristics depending upon their star formation histories.
STAR FORMATION IN H i–SELECTED GALAXIES. I. SAMPLE CHARACTERISTICS
A sample of 69 galaxies with radial velocities of less than 2500 km s À1 was selected from the H i Parkes All-Sky Survey (HIPASS) and imaged in broadband B and R and narrowband H, to deduce details about star formation in nearby disk galaxies while avoiding surface brightness selection effects. The sample is dominated by late-type, dwarf disks (mostly Sc and Sm galaxies) with exponential disk scale lengths of 1–5kpc.TheHIPASSgalaxies,onaverage,havelowerstarformationrates(SFRs),arebluer,andhavelowersurfacebrightnessthananopticallyselectedsample.Hiiregionsweredetectedinallbutoneofthegalaxies.ManygalaxieshadasfewastwotofiveHiiregions.Thegalaxies′Hequivalentwidths,colors,andSFRsperunitofHimassarebestexplainedbyyoungmeanages(1–5 kpc. The HIPASS galaxies, on average, have lower star formation rates (SFRs), are bluer, and have lower surface brightness than an optically selected sample. H ii regions were detected in all but one of the galaxies. Many galaxies had as few as two to five H ii regions. The galaxies' H equivalent widths, colors, and SFRs per unit of H i mass are best explained by young mean ages (1–5kpc.TheHIPASSgalaxies,onaverage,havelowerstarformationrates(SFRs),arebluer,andhavelowersurfacebrightnessthananopticallyselectedsample.Hiiregionsweredetectedinallbutoneofthegalaxies.ManygalaxieshadasfewastwotofiveHiiregions.Thegalaxies′Hequivalentwidths,colors,andSFRsperunitofHimassarebestexplainedbyyoungmeanages(3–5 Gyr, according to Schmidt-law models) with star formation histories in which the SFRs were higher in the past. Comparison of the surface brightness coverage of the HIPASS galaxies with that of an optically selected sample shows that such a sample may miss $10% of the local galaxy number density and could possibly miss as much as 3%–4% of the SFR density. The amount lower surface brightness galaxies contribute to the total luminosity density may be insignificant, but this conclusion is somewhat dependent on how the fluxes of these objects are determined.
The Morphology of Low Surface Brightness Disk Galaxies
The Astronomical Journal, 1995
We present U BV I and Hα images of a sample of Low Surface Brightness (LSB) disk galaxies. These galaxies are generally late types, if they can be sensibly classified at all. However, they are not dwarfs, being intrinsically large and luminous.