Circumnuclear star-forming activities along the Hubble sequence

Abstract

In order to study circumnuclear star-forming activity along the Hubble sequence, we cross-correlated the Sloan Digital Sky Survey Data Release 2 (SDSS DR2) with the Third Reference Catalog of Bright Galaxies (RC3) to derive a large sample of 1015 galaxies with both morphological and spectral information. Among these, 385 sources are classified as star-forming galaxies, and the SDSS fibre covered the circumnuclear regions (0.2−2.0 kpc). By using the spectral synthesis method to remove the contribution from the underlying old stellar population, we measured the emission lines fluxes accurately, which are then used to estimate the star-formation rates(SFRs). Our main findings are: (1) early-type spirals show much higher Hα luminosities, and hence higher SFRs, and also suffer more extinctions than late-type ones. The equivalent widths (EWs) of Hα emission lines show a similar trend; however, the very late types (Sdm ∼ Irr) do have large fractions of high EWs; (2) we confirm that D n (4000) shows a strong correlation with the strengths of metallic absorption lines (such as CN band, G band, and Mg Ib). Both these lines and the Balmer absorption lines show interesting variations between Sbc and Sd type galaxies; (3) the bar structure tightly relates to the enhanced star formation activity, an effect that is even more significant in the early-type spirals. But we should note that the bar structure is not a necessary or sufficient condition for galaxies to harbor circumnuclear star formations.

What produces the extended LINER-type emission in the NUGA galaxy NGC 5850?

“…Furthermore, it prevents us from estimating the influence of diffuse ionized gas, which can boost the Balmer emission (Blanc et al 2009), and therefore, we might overestimate the calculated SFR. Scaling the Calzetti (2012) SFR of the central SF-region to an area of 1 kpc 2 yields a SFR-density of Σ SFR ≈ 0.06 M yr −1 kpc −2 , which is lower than the median value of 0.2 M yr −1 kpc −2 for circumnuclear (0.2 kpc ≤ 2 kpc) SF in galaxies that are the same Hubble type and that are located at roughly the same distance (z = 0.00344−0.0344) (Shi et al 2006) (see also Valencia-S. et al 2012).…”

Star Formation Properties in Barred Galaxies (Sfb). I. Ultraviolet to Infrared Imaging and Spectroscopic Studies of NGC 7479

“…After the gas density becomes supercritical in the central parts, the next step is to trigger circumnuclear star formation (Sheth et al 2005); (pseudo)bulges also grow during this process (Kormendy & Kennicutt 2004). These processes have been proven by a large number of observations (e.g., Knapen et al 2006;Shi et al 2006;Gadotti 2010) and simulations (e.g., Athanassoula et al 2009). Gadotti & dos Anjos (2001) also studied the broadband UBV color profiles for 257 Sbc barred and nonbarred galaxies and found that the bulges of barred galaxies are bluer than others, indicating an increase in the star formation rate (SFR) in the central regions of these objects.…”

“…Theoretically, stellar bars can concentrate a substantial fraction of disk gas in small galactocentric radii as a result of star formation (Kormendy & Kennicutt 2004). Observations have also found that, on average, galaxies with stellar bars show higher central SFRs than unbarred galaxies (e.g., Kormendy & Fisher 2005;Fisher 2006;Shi et al 2006), and the star formation in circumnuclear regions of spiral galaxies is more dependent on stellar bars than that in their outer disks (Kennicutt 1998). Using mid-IR color to trace star formation activity, Roussel et al (2001) also found that the color distributions of strong barred galaxies show 15 μm excess, which is absent from weakly barred or unbarred galaxies.…”

Early-type galaxies with core collapse supernovae

“…The galaxy is clearly a spiral". Shi et al (2006) described it as SAa with emission line spectra. The blue integral colours (U − B = −0.04 and B − V = 0.76) of the galaxy are typical for Sb spirals (e.g., Huchra 1977).…”