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We investigated these for a sample of late-type,

It is well known that the H α luminosity is a good tracer of the star formation in a galaxy (Kennicutt 1983 ApJ, 273, 54). The Star Formation Rate (SFR) along the Hubble sequence has been studied extensively (e.g. Kennicutt 1998 ARA&A, 36, 189) and some of the main results are:

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We investigated these for a sample of late-type,

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  1. It is well known that the Hα luminosity is a good tracer of the star formation in a galaxy (Kennicutt 1983 ApJ, 273, 54). The Star Formation Rate (SFR) along the Hubble sequence has been studied extensively (e.g. Kennicutt 1998 ARA&A, 36, 189) and some of the main results are: -SFR increases for latter type galaxies a factor of 50, being the Sm and Irr those with the larger values. -Moreover, the HII regions for these galaxies are brighter (Kennicutt et al. 1989 ApJ, 435, 22) -In addition, there is a relationship between the disk averaged SFR per area and the average gas density (Kennicutt 1998). We investigated these for a sample of late-type, small (r ≤ 5 kpc), low luminous (Mb ≥ -18) galaxies (hereafter named as dwarf Spirals (dS)). They were selected from the UGC catalog (Nilson 1973) and the RC3 (de Vaucouleurs et al. 1992). For more details about the selection of the sample see Hidalgo-Gámez 2004 (Rev. Mex. A&A 40, 39). Narrow-band Hα and continuum images were obtained for a total of 18 dS galaxies at the 1.5m telescope at San Pedro Mártir observatory (Baja California, México). They were reduced and analysed using the normal procedure in MIDAS (Hidalgo-Gámez, work in progress). Does size matter...for the SFR? A.M. Hidalgo-Gámez The Hα flux were determined from the continum-subtracted Hα images, corrected from Galactic and internal extincion (only for UGC 5296). No correction for NII was implemented because the nitrogen content of these galaxies is very low, from spectra taken by the author (Hidalgo-Gámez & Ramírez-Fuentes, in preparation).. The SFR were determined following Kennicutt (1998). UGC 11820 UGC 5296 1.436 M○ pc-2 0.0011 M○ pc-2 The number of HII regions is larger, 18, as well as the SFRs, with values as large as 10-3 M○ pc-2. Now, the galaxies is located with the Sm/Im There are only 5 HII regions with SFRs between 1.6 10-4 and 10-5 M○ pc-2. These values are similar to those of Sa galaxies and to of quiescent dI (van Zee 2001, AJ 212, 2003) SFR vs.surface density plot for normal disk galaxies. The solid line corresponds to the correlation from Kennicutt (98) while the slash lines show the dispersion in such correlation. The two galaxies presented here are plotted as stars. IA-UNAM, Mexico Why the quiescent galaxies are more common among the small spirals? Here we presented the results on the SFRs of two small spiral galaxies with very similar HI content but with different size. According to Kennicutt (1998) they both should be at the same locations of the graph, and have very similar values of the SFRs. On the contrary of course, UGC 5296 is not the only quiescent galaxy in the Universe, but the caveat is that 2/3 of the 18 galaxies we have observed are quiescent. As they were selected because of their small size…..

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