The intrinsic shapes of dwarf irregular galaxies

Roychowdhury, Sambit; Chengalur, Jayaram N.; Караченцев, И. Д.; Kaisina, E. I.

doi:10.1093/mnrasl/slt123

Cited by 50 publications

(55 citation statements)

References 31 publications

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“…Moreover, S 4 G sample shows the inverse trend probably because of the large number of latetype (irregular) galaxies. However this trend is consistent with the issue of the thickening of disc towards low mass reported in recent years in the literature (Sánchez-Janssen et al 2010;Roychowdhury et al 2013).…”

Section: The Disc Thickness Versus Galactic Luminositysupporting

confidence: 93%

Does the stellar disc flattening depend on the galaxy type?

Mosenkov

Sotnikova

Решетников

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We analyze the dependence of the stellar disc flatness on the galaxy morphological type using 2D decomposition of galaxies from the reliable subsample of the Edge-on Galaxies in SDSS (EGIS) catalogue. Combining these data with the retrieved models of the edge-on galaxies from the Two Micron All Sky Survey (2MASS) and the Spitzer Survey of Stellar Structure in Galaxies (S 4 G) catalogue, we make the following conclusions:(1) The disc relative thickness z 0 /h in the near-and mid-infrared passbands correlates weakly with morphological type and does not correlate with the bulge-to-total luminosity ratio B/T in all studied bands.(2) Applying an 1D photometric profile analysis overestimates the disc thickness in galaxies with large bulges making an illusion of the relationship between the disc flattening and the ratio B/T .(3) In our sample the early-type disc galaxies (S0/a) have both flat and "puffed" discs. The early spirals and intermediate-type galaxies have a large scatter of the disc flatness, which can be caused by the presence of a bar: barred galaxies have thicker stellar discs, on average. On the other hand, the late-type spirals are mostly thin galaxies, whereas irregular galaxies have puffed stellar discs.

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Section: The Disc Thickness Versus Galactic Luminositysupporting

confidence: 93%

Does the stellar disc flattening depend on the galaxy type?

Mosenkov

Sotnikova

Решетников

et al. 2015

Monthly Notices of the Royal Astronomical Society

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“…When determining all the above three quantities, a factor equal to the measured axial ratio of the Holmberg isophote ) is used to correct for the fact that we aim to measure the surface densities perpendicular to the optical disc of the galaxy and that the optical discs of such faint dwarf galaxies are oblate spheroidal in shape (Roychowdhury et al 2013). The relative extents of the above mentioned 'stellar discs' in relation to the HI and FUV emissions can be seen in Fig.…”

Section: Estimates Of Gas and Sfr Surface Densitiesmentioning

confidence: 99%

Extended Schmidt law holds for faint dwarf irregular galaxies

Roychowdhury

Chengalur

Shi

2017

A&A

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Context. The extended Schmidt law (ESL) is a variant of the Schmidt which relates the surface densities of gas and star formation, with the surface density of stellar mass added as an extra parameter. Although ESL has been shown to be valid for a wide range of galaxy properties, its validity in low-metallicity galaxies has not been comprehensively tested. This is important because metallicity affects the crucial atomic-to-molecular transition step in the process of conversion of gas to stars. Aims. To empirically investigate for the first time whether low metallicity faint dwarf irregular galaxies (dIrrs) from the local universe follow the extended Schmidt law. Here we consider the 'global' law where surface densities are averaged over the galactic discs. Dwarf irregular galaxies are unique not only because they are at the lowest end of mass and star formation scales for galaxies, but also because they are metal-poor compared to the general population of galaxies. Methods. Our sample is drawn from the Faint Irregular Galaxy GMRT Survey (FIGGS) which is the largest survey of atomic hydrogen in such galaxies. The gas surface densities are determined using their atomic hydrogen content. The star formation rates are calculated using GALEX far ultraviolet fluxes after correcting for dust extinction, whereas the stellar surface densities are calculated using Spitzer 3.6 µm fluxes. The surface densities are calculated over the stellar discs defined by the 3.6 µm images. Results. We find dIrrs indeed follow the extended Schmidt law. The mean deviation of the FIGGS galaxies from the relation is 0.01 dex, with a scatter around the relation of less than half that seen in the original relation. In comparison, we also show that the FIGGS galaxies are much more deviant when compared to the 'canonical' Kennicutt-Schmidt relation. Conclusions. Our results help strengthen the universality of the extended Schmidt law, especially for galaxies with low metallicities. We suggest that models of star formation in which feedback from previous generations of stars set the pressure in the interstellar medium and affect ongoing star formation, are promising candidates for explaining the ESL. We also confirm that ESL is an independent relation and not a form of a relation between star formation efficiency and metallicity.

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“…The face on surface densities are computed by correcting for the inclination of the disks, assuming that they are oblate spheroids (a valid assumption considering the luminosity range of the dwarf irregular galaxies in our sample, e.g. see Roychowdhury et al 2013). We multiply the measured surface density by the cosine of the inclination angle in order to estimate the face on column density.…”

Section: Estimates Of the Gas And Star Formation Rate Densitymentioning

confidence: 99%

The relation between atomic gas and star formation rate densities in faint dwarf irregular galaxies

Roychowdhury

Chengalur

Кайсин

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We use data for faint (M B > − 14.5) dwarf irregular galaxies drawn from the FIGGS survey to study the correlation between the atomic gas density (Σ gas,atomic ) and star formation rate (Σ SFR ) in the galaxies. The estimated gas phase metallicity of our sample galaxies is Z ∼ 0.1 Z ⊙ . Understanding star formation in such molecule poor gas is of particular importance since it is likely to be of direct relevance to simulations of early galaxy formation. For about 20% (9/43) of our sample galaxies, we find that the HI distribution is significantly disturbed, with little correspondence between the optical and HI distributions. We exclude these galaxies from the comparison. We also exclude galaxies with very low star formation rates, for which stochastic effects make it difficult to estimate the true star formation rates. For the remaining galaxies we compute the Σ gas,atomic and Σ SFR averaged over the entire star forming disk of the galaxy. For these galaxies we find a nearly linear relation between the star formation rate and the atomic gas surface densities, viz. log Σ SFR = 0.91 +0.23−0.25 log Σ gas,atomic − 3.84 +0.15−0.19 . The corresponding gas consumption timescale is ∼ 10 Gyr, i.e. significantly smaller than the ∼ 100 Gyr estimated for the outer regions of spiral galaxies. We also estimate the gas consumption timescale computed using the global gas content and the global star formation rate for all galaxies with a reliable measurement of the star formation rate, regardless of whether the HI distribution is disturbed or not. The mean gas consumption timescale computed using this entire gas reservoir is ∼ 18 Gyr, i.e. still significantly smaller than that estimated for the outer parts of spirals. The gas consumption timescale for dwarfs is intermediate between the values of ∼ 100 Gyr and ∼ 2 Gyr estimated for the outer molecule poor and inner molecule rich regions of spiral disks.

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The intrinsic shapes of dwarf irregular galaxies

Cited by 50 publications

References 31 publications

Does the stellar disc flattening depend on the galaxy type?

Does the stellar disc flattening depend on the galaxy type?

Extended Schmidt law holds for faint dwarf irregular galaxies

The relation between atomic gas and star formation rate densities in faint dwarf irregular galaxies

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