Super star clusters in Hii galaxies (original) (raw)
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Analysis of the stellar population in the central area of the HII region Sh 2-284
Astronomy and Astrophysics, 2010
Context. There is a lack of state-of-the-art information on very young open clusters, with implications for determining the structure of the Galaxy. Aims. Our main objective is to study the timing and location of the star formation processes which yielded the generation of the giant HII region Sh 2-284. This includes the determination of different physical variables of the stars, such as distance, reddening, age and evolutionary stage, including pre-main-sequence (PMS) stars.
The environment of HII galaxies revisited
Astronomy & Astrophysics, 2013
We present a study of the close ( ∼ < 200h −1 75 kpc) environment of 110 relatively local (z ∼ < 0.16) HII galaxies, selected from the Sloan Digital Sky Survey (SDSS; DR7). We use available spectroscopic and photometric redshifts in order to investigate the presence of a close and possibly interacting companion galaxy. Our aim is to compare the physical properties of isolated and interacting HII galaxies and investigate possible systematic effects in their use as cosmological probes. We find that interacting HII galaxies tend to be more compact, less luminous and have a lower velocity dispersion than isolated ones, in agreement with previous studies on smaller samples. However, as we verified, these environmental differences do not affect the cosmologically important L Hβ − σ correlation of the HII galaxies.
Giant Hii regions are the most spectacular star-formin
1999
The molecular components of three giant Hii regions (NGC 5461, NGC 5462, NGC 5471) in the galaxy M101 are investigated with new observations from single dish telescopes (James Clerk Maxwell Telescope and the NRAO 12-meter) and from the Owens Valley millimeter array. Of the three Hii regions, only NGC 5461 had previously been detected in CO emission. We calculate preliminary values for the molecular mass of the GMCs in NGC 5461 by assuming a CO-to-H2 factor (X factor) and then compare these values with the virial masses. We find that the appropriate X factor is 5 times smaller than the X factor in the Milky Way despite the lower metallicity of M101. We conclude that the data in this paper demonstrate for the first time that the value of X may decrease in regions with intense star formation. The molecular mass for the association of clouds in NGC 5461 is approximately 3 × 107 M ⊙ and is accompanied by 1–2 times as much atomic mass. The observed CO emission in NGC 5461 is an order of m...
Star Cluster Complexes and the Host Galaxy in Three H II Galaxies: Mrk 36, UM 408, and UM 461
Astronomical Journal, 2011
We present a stellar population study of three H II galaxies (Mrk 36, UM 408, and UM 461) based on the analysis of new ground-based high-resolution near-infrared J, H, and Kp broadband and Brγ narrowband images obtained with Gemini/NIRI. We identify and determine the relative ages and masses of the elementary star clusters and/or star cluster complexes of the starburst regions in each of these galaxies by comparing the colors with evolutionary synthesis models that include the contribution of stellar continuum, nebular continuum, and emission lines. We found that the current star cluster formation efficiency in our sample of low-luminosity H II galaxies is ~10%. Therefore, most of the recent star formation is not in massive clusters. Our findings seem to indicate that the star formation mode in our sample of galaxies is clumpy, and that these complexes are formed by a few massive star clusters with masses gsim104 M sun. The age distribution of these star cluster complexes shows that the current burst started recently and likely simultaneously over short timescales in their host galaxies, triggered by some internal mechanism. Finally, the fraction of the total cluster mass with respect to the low surface brightness (or host galaxy) mass, considering our complete range in ages, is less than 1%.
On the structure of giant HII regions and HII galaxies
Proceedings of the International Astronomical Union, 2006
We review the structural properties of giant extragalactic HII regions and HII galaxies based on two dimensional hydrodynamic calculations, and propose an evolutionary sequence that accounts for their observed detailed structure. The model assumes a massive and young stellar cluster surrounded by a large collection of clouds. These are thus exposed to the most important star-formation feedback mechanisms: photoionization and the cluster wind. The models show how the two feedback mechanisms compete with each other in the disruption of clouds and lead to two different hydrodynamic solutions: The storage of clouds into a long lasting ragged shell that inhibits the expansion of the thermalized wind, and the steady filtering of the shocked wind gas through channels carved within the cloud stratum that results into the creation of large-scale superbubbles. Both solutions are here claimed to be concurrently at work in giant HII regions and HII galaxies, causing their detailed inner structure.
The HII galaxy environment revisited
Astronomy and Astrophysics
We present a study of the close ( ∼ < 200h −1 75 kpc) environment of 110 relatively local (z ∼ < 0.16) HII galaxies, selected from the Sloan Digital Sky Survey (SDSS; DR7). We use available spectroscopic and photometric redshifts in order to investigate the presence of a close and possibly interacting companion galaxy. Our aim is to compare the physical properties of isolated and interacting HII galaxies and investigate possible systematic effects in their use as cosmological probes. We find that interacting HII galaxies tend to be more compact, less luminous and have a lower velocity dispersion than isolated ones, in agreement with previous studies on smaller samples. However, as we verified, these environmental differences do not affect the cosmologically important L Hβ − σ correlation of the HII galaxies.
Young stellar clusters and star formation throughout the Galaxy
Astro2010 the Astronomy and Astrophysics Decadal Survey, 2009
Most stars are born in rich young stellar clusters (YSCs) embedded in giant molecular clouds. The most massive stars live out their short lives there, profoundly influencing their natal environments by ionizing HII regions, inflating wind-blown bubbles, and soon exploding as supernovae. Thousands of lower-mass pre-main sequence stars accompany the massive stars, and the expanding HII regions paradoxically trigger new star formation as they destroy their natal clouds. While this schematic picture is established, our understanding of the complex astrophysical processes involved in clustered star formation have only just begun to be elucidated. The technologies are challenging, requiring both high spatial resolution and wide fields at wavelengths that penetrate obscuring molecular material and remove contaminating Galactic field stars. We outline several important projects for the coming decade: the IMFs and structures of YSCs; triggered star formation around YSC; the fate of OB winds; the stellar populations of Infrared Dark Clouds; the most massive star clusters in the Galaxy; tracing star formation throughout the Galactic Disk; the Galactic Center region and YSCs in the Magellanic Clouds. Programmatic recommendations include: developing a 30m-class adaptive optics infrared telescope; support for high-resolution and wide field X-ray telescopes; large-aperture sub-millimeter and far-infrared telescopes; multi-object infrared spectrographs; and both numerical and analytical theory.
Stellar population in star formation regions of galaxies
Open Astronomy
We developed techniques for searching young unresolved star groupings (clusters, associations, and their complexes) and of estimating their physical parameters. Our study is based on spectroscopic, spectrophotometric, and UBVRI photometric observations of 19 spiral galaxies. In the studied galaxies, we found 1510 objects younger than 10 Myr and present their catalogue. Having combined photometric and spectroscopic data, we derived extinctions, chemical abundances, sizes, ages, and masses of these groupings. We discuss separately the specific cases, when the gas extinction does not agree with the interstellar one. We assume that this is due to spatial offset of Hii clouds with respect to the related stellar population.We developed a method to estimate age of stellar population of the studied complexes using their morphology and the relation with associated H emission region. In result we obtained the estimates of chemical abundances for 80, masses for 63, and ages for 57 young object...
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 Astrophysical Journal, 2018
We have measured the relationships between Hi mass, stellar mass and star formation rate using the Hi Parkes All Sky-Survey Catalogue (HICAT) and the Wide-field Infrared Survey Explorer (WISE). Of the 3,513 HICAT sources, we find 3.4 µm counterparts for 2,896 sources (80%) and provide new WISE matched aperture photometry for these galaxies. For our principal sample of spiral galaxies with W 1 ≤ 10 mag and z ≤ 0.01, we identify Hi detections for 93% of the sample. We measure lower Hi-stellar mass relationships that Hi selected samples that do not include spiral galaxies with little Hi gas. Our observations of the spiral sample show that Hi mass increases with stellar mass with a power-law index 0.35; however, this value is dependent on T-type, which affects both the median and the dispersion of Hi mass. We also observe an upper limit on the Hi gas fraction, which is consistent with a halo spin parameter model. We measure the star formation efficiency of spiral galaxies to be constant at 10 −9.57 yr −1 ± 0.4 dex for 2.5 orders of magnitude in stellar mass, despite the higher stellar mass spiral showing evidence of quenched star formation.