arXiv subjects

Enrico V. Held

Publications and source records attributed to Enrico V. Held.

21 records · Page 2Linked to original sources

arXiv1999

Stellar populations in the Phoenix dwarf galaxy

We have obtained deep BVI CCD photometry of Phoenix, a galaxy considered a transition case between dwarf spheroidal and dwarf irregular galaxies. A comparison of our data with the RGBs of Galactic globular clusters gives a mean metal abundance [Fe/H] = -1.81+/-0.10 dex. The presence of an intrinsic color dispersion in the upper red RGB suggests an abundance range of about 0.5 dex, although a range in age may also affect the RGB width. For the first time, a HB has been revealed at V~23.8. The HB is predominantly red yet moderately extended to the blue, which indicates the presence of a significant population with age comparable to that of old halo GGCs. This HB morphology in a metal-poor system indicates a mild "second parameter" effect. From the mean level of the HB we derived a true distance modulus 23.21+/-0.08, in good agreement with the distance modulus 23.04+/-0.07 estimated from the cutoff of the RGB at I~23.1. We find a radial gradient in the HB morphology, and our CMDs show a small number of stars above the RGB tip, that most likely are AGB stars of an intermediate age population. Their number indicates that the fraction of intermediate age population in Phoenix is approximately 30-40%. A young stellar population is definitely present in Phoenix, consistent with a star formation episode started at least 0.6 Gyr ago, up to 1x10^{8} yr ago. Both young stars and AGB stars are centrally concentrated, which indicates that recent star formation preferentially occurred in the inner galaxy regions. In many respects, Phoenix appears not dissimilar from dwarf spheroidal galaxies in the Local Group.

astro-ph↗

arXiv1996

CCD photometry of the Tucana dwarf galaxy

We present $V$ and $I$ CCD photometry for $\sim360$ stars in the recently discovered dwarf galaxy Tucana. The large field investigated and the accurate photometric calibration make our data complementary to the deeper HST photometry. From the $I$ magnitude of the tip of the red giant branch we estimate a distance modulus $(m-M)_0=24.69\pm0.16$, corresponding to $870\pm60$ Kpc, confirming that Tucana is an isolated dwarf spheroidal located almost at the border of the Local Group. From the color of the red giant branch tip and by direct comparison with the giant branches of galactic globular clusters we estimate a metallicity [Fe/H]=$-1.8\pm0.2$, with no clear indication for a metallicity spread. The color--magnitude diagram indicates that Tucana has had a single star formation burst at the epoch of the Galactic globular cluster star formation. There is no evidence for an intermediate or young stellar population. We derive the V luminosity profile, the surface density profile of resolved stars, and the structural parameters of Tucana, from which we confirm that Tucana participates to the general metallicity--surface brightness--absolute magnitude relations defined by the Galaxy and M31 dwarf spheroidal and dwarf elliptical companions.

astro-ph↗

arXiv1993

Spectroscopy of Dwarf Elliptical Galaxies in the Fornax Cluster

We present the results of spectroscopic observations of 10 nucleated dwarf elliptical galaxies (dE's) in the Fornax cluster. The blue spectra of Fornax dE galaxies indicate a wide range of metallicities at a given luminosity, similar to those of intermediate to \it metal-rich globular clusters. Metal abundances derived in this paper are well correlated with optical colors and agree with previous spectroscopic results. A discrepancy with metallicities inferred from infrared colors is evident; possible causes include an intermediate age population and dilution of spectral features by a blue light excess. Dwarf ellipticals exhibit a wide variation of hydrogen line strength which points to a complex star formation history. Prominent Balmer absorption lines are the signature of a young stellar population in the nuclei of some (but not all) dE's, while moderately strong Balmer lines in relatively metal-rich dE's are more consistent with an extended main sequence. The velocity distribution of the Fornax dwarfs is flatter than that of brighter galaxies at the 75\% confidence level, possibly indicating a difference in the kinematics of the two samples.

astro-ph↗