Morphological properties of galaxies in different Local Volume environments

Abstract

We consider an all-sky sample of 1029 Local Volume (LV) galaxies situated within a distance of 11 Mpc. Their majority have precise distances, estimates of hydrogen mass fraction and star-formation rate derived from far-ultraviolet or H α fluxes. To describe an environment, we attribute two dimensionless values: the density contrast created by the most significant neighbour and the local density contrast produced by all neighbours within a separation of 1 Mpc. The hydrogen mass fraction exhibits a weak effect of H i deficiency being the most pronounced for dwarf irregular galaxies. The specific star-formation rate (sSFR) is more sensitive to the environment than the hydrogen mass fraction. Almost all (99 per cent) LV galaxies have their sSFR below −9.4 dex (yr −1 ). We notice that irregular dwarfs as well as late-type bulgeless galaxies are capable to reproduce their stellar mass with the observed sSFR over the cosmic time. Thus, the transformation of gas into stars in dIrs and spiral disks is rather sluggish unlike that in E, S0, dSph galaxies, whose star-formation history has been stormy and short. Scatter of SFR(H α)-to-SFR(FUV) ratio increases from Sc, Sd, Sm galaxies towards BCD, Im, Ir types that favours the idea of bursty star formations in low-mass galaxies. However, this bursty activity is caused rather by internal processes than by an external tidal action. A fraction of quenched E, S0, dSph galaxies increases from ∼ 5 per cent in the field up to ∼ 50 per cent in the densest regions.

Star Formation in Nearby Dwarf Galaxies

“…We combined the above star-formation rate estimates in LV galaxies with similar data for other galaxies located within 11 Mpc. It was already pointed out in Ricciardelli et al [35] and Karachentsev et al [36] that the SFR in late-type galaxies depends only slightly on the neighborhood. The trend of the decrease of SFR from isolated galaxies to group members barely exceeds the dispersion of this quantity and is most manifested among the least massive dwarf galaxies.…”

Ha Images of Ultra-Flat Edge-On Spiral Galaxies

“…This approach is free from iterations, however, it is applicable only to galaxies with a known rotation amplitude. Considering the statistics of the relation SF R(Hα)/SF R(F U V ) for the Local Volume galaxies, Karachentsev et al (2018) concluded that expression (6) somewhat overestimates the extinction in massive galaxies and underestimates it for dwarf galaxies. In our estimation, the appropriate correction for the internal extinction in late-type spiral disks has the form…”

Dwarf Galaxies in the Local Volume

“…We already pointed out above that the closer the dwarf galaxy is to its massive neighbor, the lower is its gas content. The effect of the ambient density on the relative content of hydrogen mass in LV galaxies was analyzed in detail in [53]. To estimate the ambient density, the above authors used three different dimensionless parameters: Θ 1 , the relative local density created by the most circles.…”

“…(b) The SF R(Hα)/SF R(F U V ) ratio on the average decreases from spirals to progressively less Dependence of the SF R(Hα)/SF R(F U V ) ratio on other parameters apparent axial ratio of the galaxy, its morphological type, ambient density were analyzed in [53].…”