arXiv subjects

Max Pettini

Publications and source records attributed to Max Pettini.

186 records · Page 11Linked to original sources

arXiv1996

Complex Mg II absorption in the outer disk of M61

The increasing availability of high quality spectra of QSO absorption line systems at resolutions of only a few km/s is expected to facilitate the translation of the kinematics of components comprising the lines into the spatial distribution of gas around an absorbing galaxy. In this Letter, we present Hubble Space Telescope (HST) spectra of Q1219+047, a QSO whose sightline passes 21 h-1 kpc from the center of M61, through the outer regions of an extended H I disk. We detect complex Mg II absorption, spanning a velocity range of approximately 300 km/s, and strong C IV absorption; these are the first UV observations of a QSO absorption line system arising in the outskirts of a disk of a nearby galaxy at low inclination. Our observations are at odds with models of galaxies in which absorbing clouds co-rotate with a galaxy's disk, because M61's low inclination should give rise to only a few Mg II components spread over a small velocity range in such a model. Hence our results throw doubt on whether absorption line profiles can be used to infer the spatial distribution of gas around absorbing galaxies.

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arXiv1996

Dust in High Redshift Galaxies

Measurements of Zn and Cr abundances in damped Lyman alpha systems at absorption redshifts between 0.692 and 3.390 show that metals and dust are much less abundant in high redshift galaxies than in the Milky Way today. We conclude that the overall degree of metal enrichment of DLA galaxies approximately 13.5 Gyr ago is 1/15 solar. The depletion of Cr is approximately 2, significantly less than in local interstellar clouds. We propose this reflects an overall lower abundance of dust, and deduce a typical dust-to-gas ratio of 1/30 of the Milky Way value, still sufficient to explain the weakness of Lyman alpha emission from star-forming regions. We show that, despite claims to the contrary, these conclusions are not inconsistent with recent high resolution observations of DLAs with the Keck Telescope.

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arXiv1995

On the Oxygen Abundance of Neutral Gas in I Zw 18

Whether the H II regions of dwarf emission-line galaxies are self-polluted by the nucleosynthetic products of massive stars remains an open question, despite recent claims to the contrary. We show that the finding by Kunth and collaborators that the neutral interstellar medium of I Zw 18 has a metallicity one order of magnitude lower than that of the ionized gas is highly uncertain. The range of possible values of (O/H) admitted by the saturated O I absorption line used in their analysis is very large, spanning a factor of the order of 1000. We suggest that future observations of the intrinsically weaker S II 1256 multiplet offer the best prospects for measuring the true degree of metal enrichment of this dwarf galaxy.

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arXiv1995

Lyman alpha Emission from High-Redshift Galaxies

We summarise the results of a deep search for Lyman alpha emission from star-forming regions associated with damped Lyman alpha absorption systems and conclude that the Lyman alpha luminosity of high redshift galaxies is generally less than 10^(42) erg/s . We also present a newly discovered case, in the field of the QSO Q2059-360, where the emission is unusually strong, possibly because the damped system is close in redshift to the QSO.

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arXiv1995

Element Abundances at High Redshifts: The N/O Ratio in a Primeval Galaxy

The damped Lyman alpha systems seen in the spectra of high redshift QSOs offer the means to determine element abundances in galaxies observed while still at an early stage of evolution. Such measurements, which have only recently come within reach, complement and extend the data provided by studies of different stellar populations in our Galaxy and of extragalactic H~II regions which have up to now formed the basis of galactic chemical evolution models. In this paper we demonstrate the potential of this new approach with high-resolution echelle observations of several elements in the z(abs) = 2.27936 absorption system in the bright z(em) = 2.940 QSO 2348-147. The absorbing galaxy appears to be chemically unevolved, with heavy element abundances only 1/100 of solar; if it is the progenitor of a spiral galaxy like our own, it is unlikely to have collapsed to form a thin disk by z = 2.3 (corresponding to a look-back time of approximately 13 Gyr for H_0 = 50 km/s/Mpc and q_0 = 0.01). Our data allow us to measure the nitrogen-to-oxygen ratio at a metallicity lower than those of the most metal-poor dwarf galaxies known. We find that, relative to the solar scale, N is more underabundant than O by at least a factor of 15. This result is broadly in line with current ideas on the relative importance of primary and secondary production of N; future measurements in several damped Lyman alpha systems will permit more stringent tests of models for the evolution of the N/O ratio with time. Oxygen and other alpha-elements are overabundant relative to Fe by no more than the factor of about 3 typical of metal-poor stars in the disk and halo of the Milky Way.

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arXiv1994

Interstellar Titanium in the Galactic Halo

We present observations of Ti~II~$λ3384$ absorption towards 15 distant stars in the Galactic halo and the Magellanic Clouds. These new data extend existing surveys of the distribution of Ti$^+$ to larger distances from the plane of the Galaxy than sampled previously, allowing the scale height of titanium to be determined for the first time. We find $h_{Ti^+} = 1.5 \pm 0.2$~kpc, a value which although greater than those of other tracers of neutral gas, is not as large as had been suspected. We interpret the extended distribution of Ti$^+$ as an indication that its severe depletion in interstellar clouds in the disk is reduced at the lower densities prevailing in the halo. The data are consistent with a simple power-law dependence of the Ti abundance on the ambient density, with exponent $k \simeq -1$. If the model is correct, it implies that refractory elements like Ti are fully returned to the gas phase at distances beyond $\sim 1$ kpc from the plane of the Galaxy.

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