The Protostellar Luminosity Function

The protostellar luminosity function (PLF) is the present-day luminosity function of the protostars in a region of star formation. It is determined using the protostellar mass function (PMF) in combination with a stellar evolutionary model that provides the luminosity as a function of instantaneous and final stellar mass. As in McKee & Offner (2010), we consider three main accretion models: the Isothermal Sphere model, the Turbulent Core model, and an approximation of the Competitive Accretion model. We also consider the effect of an accretion rate that tapers off linearly in time and an accelerating star formation rate. For each model, we characterize the luminosity distribution using the mean, median, maximum, ratio of the median to the mean, standard deviation of the logarithm of the luminosity, and the fraction of very low luminosity objects. We compare the models with bolometric luminosities observed in local star forming regions and find that models with an approximately constant accretion time, such as the Turbulent Core and Competitive Accretion models, appear to agree better with observation than those with a constant accretion rate, such as the Isothermal Sphere model. We show that observations of the mean protostellar luminosity in these nearby regions of low-mass star formation suggest a mean star formation time of 0.3$pm$0.1 Myr. Such a timescale, together with some accretion that occurs non-radiatively and some that occurs in high-accretion, episodic bursts, resolves the classical luminosity problem in low-mass star formation, in which observed protostellar luminosities are significantly less than predicted. An accelerating star formation rate is one possible way of reconciling the observed star formation time and mean luminosity.

Evolution of the Halpha luminosity function

The Smithsonian Hectospec Lensing Survey (SHELS) is a window on the star formation history over the last 4 Gyr. SHELS is a spectroscopically complete survey for Rtot < 20.3 over 4 square degrees. We use the 10k spectra to select a sample of pure star forming galaxies based on their Halpha emission line. We use the spectroscopy to determine extinction corrections for individual galaxies and to remove active galaxies in order to reduce systematic uncertainties. We use the large volume of SHELS with the depth of a narrowband survey for Halpha galaxies at z ~ 0.24 to make a combined determination of the Halpha luminosity function at z ~ 0.24. The large area covered by SHELS yields a survey volume big enough to determine the bright end of the Halpha luminosity function from redshift 0.100 to 0.377 for an assumed fixed faint-end slope alpha = -1.20. The bright end evolves: the characteristic luminosity L* increases by 0.84 dex over this redshift range. Similarly, the star formation density increases by 0.11 dex. The fraction of galaxies with a close neighbor increases by a factor of 2-5 for L(Halpha) >~ L* in each of the redshift bins. We conclude that triggered star formation is an important influence for star forming galaxies with Halpha emission.

The K-Band Galaxy Luminosity Function

We measured the K-band luminosity function using a complete sample of 4192 morphologically-typed 2MASS galaxies with 7 < K < 11.25 mag spread over 2.12 str. Early-type (T < -0.5) and late-type (T > -0.5) galaxies have similarly shaped luminosity functions, alpha_e=-0.92+/-0.10 and alpha_l=-0.87+/-0.09. The early-type galaxies are brighter, M_*e=-23.53+/-0.06 mag compared to M_*l=-22.98pm0.06 mag, but less numerous, n_*e=(0.0045+/-0.0006)h^3/Mpc^3 compared to n_*l=(0.0101+/-0.0013)h^3/Mpc^3 for H_0=100h km/s Mpc, such that the late-type galaxies slightly dominate the K-band luminosity density, j_late/j_early=1.17+/-0.12. Our morphological classifications are internally consistent, consistent with previous classifications and lead to luminosity functions unaffected by the estimated uncertainties in the classifications. These luminosity functions accurately predict the K-band number counts and redshift distributions for K < 18 mag, beyond which the results depend on galaxy evolution and merger histories.

The Composite Luminosity Function of A496

Deep photometric observations in three colours of the cluster A 496 show that the luminosity function is bimodal with a deep gap at g about 19.0. That is there is a net separation between E/SO galaxies that are nicely fitted by a gaussian distribution curve and the dwarfs that better match a Shechter Function. This is the first cluster observed and reduced out of a sample of 19 clusters which we have in our program. However comparison with the data of Virgo and Coma might suggest a correlation between cluster morphology and amplitude of the two distribution: Normal and dwarf population. This would have strong implication for the understanding of cluster formation and evolution so that we are pursuing the estimate of the LF in various colours and to faint magnitudes both for low and high redshift clusters.

The properties and luminosity function of extremely low luminosity galaxies

We examine a sample of low redshift (10 < d < 150 Mpc) galaxies including galaxies with r-band absolute magnitudes as faint as -12.5 (for h=1), selected from the Sloan Digital Sky Survey Data Release 2 (SDSS). The sample is unique in containing galaxies of extremely low luminosities in a wide range of environments, selected with uniform and well-understood criteria. We present the luminosity function as well as the broad-band properties of low luminosity galaxies in this sample. A Schechter function is an insufficient parameterization of the r-band luminosity function; there is an upturn in the slope at low luminosities. The resulting slope at low luminosities in this sample is around -1.3. However, we almost certainly miss a large number of galaxies at very low luminosities due to low surface brightness selection effects, and we estimate that the true low luminosity slope may be as steep or steeper than -1.5. The results here are consistent with previous SDSS results and, in the g-band, roughly consistent with the results of the Two degree Field Galaxy Redshift Survey. Extremely low luminosity galaxies are predominantly blue, low surface brightness, exponential disks.