A Variation in the Present Star Formation Activity of Spiral Galaxies

Abstract

The star formation rate in spiral galaxies is considered to be decreasing continuously with time in a time scale of 10 9 yr. The present star formation activity, on the other hand, occurs in molecular clouds with a time scale of 10 7 yr, and shows various degrees among galaxies. We make a new data set of 1681 nearby spiral galaxies from available databases and study the statistics of the present star formation activity. We analyze far-infrared and optical B-band surface brightnesses of the H II regions and the non-H II regions in M 31 and show that a far-infrared-to-optical B-band flux ratio, f FIR /f B , is a useful indicator of the present star formation activity of spiral galaxies. For the sample galaxies, we make the distribution diagram of log (f FIR /f B ) versus log L B for each morphological type. The distribution of f FIR /f B has a dispersion of one to two orders of magnitude even within the same morphological type of galaxies, implying that the star formation activities of spiral galaxies changes discontinuously in a short time scale. Analyzing the log (f FIR /f B ) versus log L B correlation, we suggest that the most active star formation in galaxies does not continue longer than 10 8 yr. We also construct a universal distribution histogram of log (f FIR /f B ) for each morphological type. The earlier-type spirals tend to show larger variation of the present star formation activity. We discuss the correlation between the present star formation activity and the structures and environments of galaxies. We suggest that the short-term variation occurs primarily due to internal processes which may change with the morphological type of galaxies.

Star Formation in the [ITAL]Infrared Space Observatory[/ITAL] Atlas of Bright Spiral Galaxies

“…Both these studies used RSA morphological classifications, and as we have argued above, trends found in samples classified with the RSA catalog will at least partly reflect the classification criteria rather than true physical trends. The remaining photometric infrared studies, including ), de Jong et al (1984, Devereux & Young (1991), Isobe & Feigelson (1992), Tomita et al (1996), and Devereux & Hameed (1997), found no significant correlation between star formation activity and Hubble type. We suggest that the advantages the ISO measurements provide, both the angular resolution and the point-and-integrate observing mode, compared with IRAS, and the normalization by K-band fluxes rather than by Bband fluxes, are responsible for the different conclusions reached in this study compared with most of the previous infrared studies.…”

Star Formation in Galaxies Along the Hubble Sequence

“…Figure 4 shows the expected trend toward stronger FIR emission with later Hubble type, but the trend is considerably weaker, in the sense that early-type galaxies show much higher FIR luminosities than would be expected given their UV-visible spectra. Comparisons of L F IR /L B distributions show almost no dependence on Hubble type at all (Isobe & Feigelson 1992, Tomita et al 1996, Devereux & Hameed 1997, but this is misleading because the B-band luminosity itself correlates with the SFR (see Figure 2). …”

“…Comprehensive analyses of the global SFRs of galaxies have been carried out using Hα surveys (Kennicutt 1983a, Caldwell et al 1991, Young et al 1996, UV continuum surveys (Donas et al 1987, Deharveng et al 1994, FIR data (Sauvage & Thuan 1992, Walterbos & Greenawalt 1996, Tomita et al 1996, Devereux & Hameed 1997, and multi-wavelength surveys (Gavazzi & Scodeggio 1996. The absolute SFRs in galaxies, expressed in terms of the total mass of stars formed per year, show an enormous range, from virtually zero in gas-poor elliptical, S0, and dwarf galaxies to ∼20 M ⊙ yr −1 in gas-rich spirals.…”

The Hαgalaxy survey

“…The impact of the presence of a bar on the total SFR in a galaxy has been studied by many authors (e.g., Hawarden et al 1986;Dressel 1988;Puxley et al 1988;Pompea & Rieke 1990;Isobe & Feigelson 1992;Ryder & Dopita 1994;Tomita et al 1996;Huang et al 1996;Martinet & Friedli 1997;Aguerri 1999;Sheth et al 2002;Roussel et al 2001;Verley et al 2007), but no consensus has been reached as to whether the presence of bars causes a global enhancement of the SFR.…”