Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Star Formation Rate Intensity Distribution Function -- Comparison of Observations with Hierarchical Galaxy Formation
92
0
0.0
(
0
)
Authors
Rennan Barkana
Ask ChatGPT about the research
No Arabic abstract
Recently, Lanzetta et al. (2002) have measured the distribution of star formation rate intensity in galaxies at various redshifts. This data set has a number of advantages relative to galaxy luminosity functions; the effect of surface-brightness dimming on the selection function is simpler to understand, and this data set also probes the size distribution of galactic disks. We predict this function using semi-analytic models of hierarchical galaxy formation in a LCDM cosmology. We show that the basic trends found in the data follow naturally from the redshift evolution of dark matter halos. The data are consistent with a constant efficiency of turning gas into stars in galaxies, with a best-fit value of 2%, where dust obscuration is neglected; equivalently, the data are consistent with a cosmic star formation rate which is constant to within a factor of two at all redshifts above two. However, the practical ability to use this kind of distribution to measure the total cosmic star formation rate is limited by the predicted shape of an approximate power law with a smoothly varying power, without a sharp break.
rate research
Read More
We present total infrared (IR) and ultraviolet (UV) luminosity functions derived from large representative samples of galaxies at z ~ 0, selected at IR and UV wavelengths from the IRAS IIFSCz catalogue, and the GALEX AIS respectively. We augment these with deep Spitzer and GALEX imaging of galaxies in the 11 Mpc Local Volume Legacy Survey (LVL), allowing us to extend these luminosity functions to lower luminosities (~10^6 L_sun), and providing good constraints on the slope of the luminosity function at the extreme faint end for the first time. Using conventional star formation prescriptions, we generate from our data the SFR distribution function for the local Universe. We find that it has a Schechter form, that the faint-end slope has a constant value (to the limits of our data) of {alpha} = -1.51 pm 0.08, and the characteristic SFR is 9.2 M_sun/yr. We also show the distribution function of the SFR volume density; we then use this to calculate a value for the total SFR volume density at z ~ 0 of 0.025 pm 0.0016 M_sun/yr/Mpc^-3, of which ~ 20% is occurring in starbursts. Decomposing the total star formation by infrared luminosity, it can be seen that 9 pm 1% is due to LIRGs, and 0.7 pm 0.2% is occuring in ULIRGs. By comparing UV and IR emission for galaxies in our sample, we also calculate the fraction of star formation occurring in dust obscured environments, and examine the distribution of dusty star formation: we find a very shallow slope at the highly extincted end, which may be attributable to line of sight orientation effects as well as conventional internal extinction.
This letter matches the shape of the star formation intensity distribution function to empirical laws such as the Schmidt law. The shape of the distribution at a redshift of one is reproduced from the empirical Schmidt law with a critical density, a Schechter distribution of galaxy masses and the assumption that star formation occurs mainly in exponential disks. The shape of the distribution depends primarily on two values, the characteristic mass m* in the Schechter mass distribution and the characteristic radius re in the exponential disk. As these characteristic values evolve they will affect the shape of the distribution function. The expected direction of evolution of the parameters partially cancels each other leaving the distribution shape relatively invariant.
We describe the GALFORM semi-analytic model for calculating the formation and evolution of galaxies in hierarchical models. It improves upon, and extends, the Cole et al 1994 model. The model employs a new Monte-Carlo algorithm to follow the merging evolution of dark matter halos with arbitrary mass resolution. It incorporates realistic descriptions of the density profiles of dark matter halos and their gas content; follows the chemical evolution of gas and stars, and the associated production of dust; and includes a detailed calculation of the sizes of disks and spheroids. Wherever possible, our prescriptions for modelling individual physical processes are based on results of numerical simulations. We apply our methods to the LCDM cosmology (Omega_0=0.3, Lambda_0=0.7), and find good agreement with a wide range of properties of the local galaxy population: the B-band and K-band luminosity functions, the distribution of colours for the population as a whole, the ratio of ellipticals to spirals, the distribution of disk sizes, and the current cold gas content of disks. (Abridged)
We present a detailed clustering analysis of the young stellar population across the star-forming ring galaxy NGC 6503, based on the deep HST photometry obtained with the Legacy ExtraGalactic UV Survey (LEGUS). We apply a contour-based map analysis technique and identify in the stellar surface density map 244 distinct star-forming structures at various levels of significance. These stellar complexes are found to be organized in a hierarchical fashion with 95% being members of three dominant super-structures located along the star-forming ring. The size distribution of the identified structures and the correlation between their radii and numbers of stellar members show power-law behaviors, as expected from scale-free processes. The self-similar distribution of young stars is further quantified from their autocorrelation function, with a fractal dimension of ~1.7 for length-scales between ~20 pc and 2.5 kpc. The young stellar radial distribution sets the extent of the star-forming ring at radial distances between 1 and 2.5 kpc. About 60% of the young stars belong to the detected stellar structures, while the remaining stars are distributed among the complexes, still inside the ring of the galaxy. The analysis of the time-dependent clustering of young populations shows a significant change from a more clustered to a more distributed behavior in a time-scale of ~60 Myr. The observed hierarchy in stellar clustering is consistent with star formation being regulated by turbulence across the ring. The rotational velocity difference between the edges of the ring suggests shear as the driving mechanism for this process. Our findings reveal the interesting case of an inner ring forming stars in a hierarchical fashion.
The distributions of size and luminosity for star-forming regions in the nearby spiral galaxy NGC 628 are studied over a wide range of scales using progressively blurr
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
