The Relationship Between Gas, Stars, and Star Formation in Irregular Galaxies: A Test of Simple Models

نویسنده

  • Deidre A. Hunter
چکیده

Irregular galaxies are a unique test of models for the physical laws regulating star formation because of their lack of spiral density waves and rotational shear. Here we explore various instability models for the onset of star formation in irregular galaxies. If the gas is unstable, clouds and eventually stars can form, and so these models should predict where star formation occurs. Critical gas densities were calculated for gravitational instabilities in two models, one with a thin, pure-gas disk (Σc), and another with a thick disk composed of gas and a star-like fluid (Σc,2f ). We also calculated the stability properties of three dimensional systems including dark matter, considered the thermal state of the gas, and used a modified threshold column density written in terms of the local rate of shear instead of the epicyclic frequency. The model predictions were compared to the azimuthally-averaged present day star formation activity traced by the Hα surface brightness, and to the 1 Gyr-integrated star formation activity represented by the stellar surface brightness. We find that the ratio of the observed gas density to the critical gas density, Σg/Σc, is lower by a factor of ∼ 2 in most of the Im galaxies than it is in spiral galaxies, at both the intermediate radii where Σg/Σc is highest, and at the outer radii where star formation ends. We also find that, although star formation in irregulars usually occurs at intermediate radii where Σg/Σc is highest, this activity often ends before Σg/Σc drops significantly in the outer regions, and it remains high in the inner regions where

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Stellar Populations in the Central Galaxies of Fossil Groups

It is inferred from the symmetrical and luminous X-ray emission of fossil groups that they are mature, relaxed galaxy systems. Cosmological simulations and observations focusing on their dark halo and inter-galactic medium properties confirm their early formation. Recent photometric observations suggest that, unlike the majority of non-fossil brightest group galaxies (BGGs), the central early-t...

متن کامل

Star Formation in Isolated Disk Galaxies. I. Models and Star Formation Characteristics

We model star formation in a wide range of isolated disk galaxies composed of a dark matter halo and a disk of stars and isothermal gas, using a threedimensional smoothed particle hydrodynamics code. Absorbing sink particles are used to directly measure the mass of gravitationally collapsing gas. They reach masses characteristic of stellar clusters. In this paper, we describe our galaxy models ...

متن کامل

Pulsating red giant and supergiant stars in the Local Group dwarf galaxy Andromeda I

We have conducted an optical long-term monitoring survey of the majority of dwarf galaxies in the Local Group, with the Isaac Newton Telescope (INT), to identify the long period variable (LPV) stars. LPV stars vary on timescales of months to years, and reach the largest amplitudes of their brightness variations at optical wavelengths, due to the changing temperature. They trace stellar populati...

متن کامل

1 v 1 1 A ug 1 99 8 The Recent Star Formation in Sextans A

We investigate the relationship between the spatial distributions of stellar populations and of neutral and ionized gas in the Local Group dwarf irregular galaxy Sextans A. This galaxy is currently experiencing a burst of localized star formation, the trigger of which is unknown. We have resolved various populations of stars via deep UBV (RI)C imaging over an area with diameter ∼ 5.3. We have c...

متن کامل

The Universal Stellar Mass–stellar Metallicity Relation for Dwarf Galaxies

We present spectroscopic metallicities of individual stars in seven gas-rich dwarf irregular galaxies (dIrrs), and we show that dIrrs obey the same mass–metallicity relation as the dwarf spheroidal (dSph) satellites of both the Milky Way and M31: Z∗ ∝ M 0.30±0.02 ∗ . The uniformity of the relation is in contradiction to previous estimates of metallicity based on photometry. This relationship is...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 1997