SIMBAD references

2000ApJ...538..569R - Astrophys. J., 538, 569-580 (2000/August-1)

Lopsided galaxies, weak interactions, and boosting the star formation rate.


Abstract (from CDS):

To investigate the link between weak tidal interactions in disk galaxies and the boosting of their recent star formation, we obtain images and spatially integrated spectra (3615 Å≤λ≤5315 Å) for 40 late-type spiral galaxies (Sab-Sbc) with varying degrees of lopsidedness (a dynamical indicator of weak interactions). We quantify lopsidedness as the amplitude <A{d5}1> of the m=1 Fourier component of the azimuthal surface brightness distribution averaged over a range of radii. The median spectrum of the most lopsided galaxies shows strong evidence for a more prominent young stellar population (i.e., strong Balmer absorption, strong nebular emission, a weak 4000 Å break, and a blue continuum) when compared to the median spectrum of the most symmetric galaxies. We compare the young stellar content, quantified by EW(Hδabs) and the strength of the 4000 Å break (D4000), with lopsidedness and find a 3-4 σ correlation between the two. We also find a 3.2 σ correlation between EW(Hβemission) and lopsidedness. Using the evolutionary population synthesis code of Bruzual & Charlot we model the spectra as an ``underlying population'' and a superimposed ``boost population'' with the aim of constraining the fractional boost in the SFR averaged over the past 0.5 Gyr (the characteristic lifetime of lopsidedness). From the difference in both EW(Hδabs) and the strength of the 4000 Å break (D4000) between the most and least symmetric thirds of our sample, we infer that ∼1x109 M of stars are formed over the duration of a lopsided event in addition to the ``underlying'' star formation history (assuming a final galactic stellar mass of 1010 M). This corresponds to a factor of 8 increase in the star formation rate over the past 5x108 years. For the nuclear spectra, all of the above correlations except D4000 versus <A{d5}1> are weaker than for the disk, indicating that in lopsided galaxies, the star formation boost is not dominated by the nucleus.

Abstract Copyright:

Journal keyword(s): Galaxies: Evolution - Galaxies: Interactions - Galaxies: Kinematics and Dynamics - Galaxies: Spiral - Galaxies: Structure - Stars: Formation

Simbad objects: 40

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