We present a new technique to quantify the light contribution coming from the faint high redshift ($zsim6$) galaxies below the detection threshold of imaging data, set conventionally at S/N=4.5. We illustrate the technique with an application to Hubb
le Space Telescope Advanced Camera for Surveys images in the F775W and F850LP filters of the Ultra Deep Field parallel field NICP12. The aim of this analysis is to extend by a few magnitudes the faint end of the luminosity function at $zsim6$. After masking all the detected sources in the field we apply a Fast Fourier Transform to obtain the spatial power spectrum of the background signal. The power spectrum permits us to separate the background noise signal, the residuals due to the data reduction of the wide field, and the overall signal produced by faint galaxies. The ratio of the signal in the i_775 and z_850 bands is used to estimate the contribution of the faint i-dropout objects. We rely on extensive Monte Carlo simulations to characterize various sources of uncertainty and quantify the number of faint i-dropout galaxies in the field. The analysis allows us to put constraints on the luminosity function at $zsim6$ down to z_850= 30 mag, 2.5 mag fainter than with standard techniques on the same data. The data are consistent with a faint end slope of the luminosity function of $alpha = -1.9$. Assuming a specific set of values for the clumping factor, escape fraction, and spectral energy distribution, we find that the $zsim6$ undetected galaxies down to z_850=30 mag could have driven cosmic reionization.
The near-infrared (NIR) wavelength range offers some unique spectral features, and it is less prone to the extinction than the optical one. Recently, the first flux calibrated NIR library of cool stars from the NASA Infrared Telescope Facility (IRTF)
have become available, and it has not been fully exploited yet. We want to develop spectroscopic diagnostics for stellar physical parameters based on features in the wavelength range 1-5 micron. In this work we test the technique in the I and K bands. The study of the Y, J, H, and L bands will be presented in the following paper. An objective method for semi-empirical definition of spectral features sensitive to various physical parameters is applied to the spectra. It is based on sensitivity map--i.e., derivative of the flux in the spectra with respect to the stellar parameters at a fixed wavelength. New optimized indices are defined and their equivalent widths (EWs) are measured. A number of sensitive features to the effective temperature and surface gravity are re-identified or newly identified clearly showing the reliability of the sensitivity map analysis. The sensitivity map allows to identify the best bandpass limits for the line and nearby continuum. It reliably predicts the trends of spectral features with respect to a given physical parameter but not their absolute strengths. Line blends are easy to recognize when blended features have different behavior with respect to some physical stellar parameter. The use of sensitivity map is therefore complementary to the use of indices. We give the EWs of the new indices measured for the IRTF star sample. This new and homogeneous set of EWs will be useful for stellar population synthesis models and can be used to get element-by-element abundances for unresolved stellar population studies in galaxies.
The detection of gamma-rays from dark matter (DM) annihilation is among the scientific goals of the Fermi Large Area Telescope (formerly known as GLAST) and Cherenkov telescopes. In this paper we investigate the existence of realistic chances of such
a discovery selecting some nearby dwarf spheroidal galaxies (dSph) as a target. We study the detectability with the Fermi-LAT of the gamma-ray flux from DM annihilation in Draco, Ursa Minor, Carina, and Sextans, for which the state-of-art DM density profiles were available. We assume the DM is made of Weakly Interacting Massive Particles such as the Lightest Supersymmetric Particle (LSP) and compute the expected gamma-ray flux for optimistic choices of the unknown underlying particle physics parameters. We then compute the boost factors due to the presence of DM clumps and of a central supermassive black hole. Finally, we compare our predictions with the Fermi-LAT sensitivity maps. We find that the dSph galaxies shine above the Galactic smooth halo: e.g., the Galactic halo is brighter than the Draco dSph only for angles smaller than 2.3 degrees above the Galactic Center. We also find that the presence of a cusp or a constant density core in the DM mass density profile does not produce any relevant effect in the gamma-ray flux due to the fortunate combination of the geometrical acceptance of the Fermi-LAT detector and the distance of the galaxies and that no significant enhancement is given by the presence of a central black hole or a population of sub-subhalos. We conclude that, even for the most optimistic scenario of particle physics, the gamma-ray flux from DM annihilation in the dSph galaxies of the LG would be too low to be detected with the Fermi-LAT.
(abridged) Photometry and long-slit spectroscopy are presented for a sample of 6 galaxies with a low surface brightness stellar disc and a bulge. The stellar and ionised-gas kinematics were measured along the major and minor axis in half of the sampl
e galaxies, whereas the other half was observed only along two diagonal axes. Spectra along two diagonal axes were obtained also for one of the objects with major and minor axis spectra. The kinematic measurements extend in the disc region out to a surface-brightness level mu_R~24mag/arcsec^2 reaching in all cases the flat part of the rotation curve. The stellar kinematics turns out to be more regular and symmetric than the ionised-gas kinematics, which often shows the presence of non-circular, off-plane, and non-ordered motions. This raises the question about the reliability of the use of the ionised gas as the tracer of the circular velocity in the modeling of the mass distribution, in particular in the central regions of low surface brightness galaxies.
The photometric and kinematic properties of Sb NGC 1292 suggest it hosts a pseudobulge. The properties of the stellar population of such a pseudobulge are consistent with a slow buildup within a scenario of secular evolution.
We present integral-field spectroscopy of the ionized gas in the central regions of four galaxies with a low surface brightness disk taken with the Visible Multi Object Spectrograph at the Very Large Telescope and aimed at testing the accuracy in the
determination of the central logarithmic slope $alpha$ of the mass density radial profile $rho(r) propto r^alpha$ in this class of objects. For all the sample galaxies we subtracted from the observed velocity field the best-fit model of gas in circular motions and derived the residuals. Only ESO-LV 5340200 is characterized by a regular velocity field. We extracted the velocity curves of this galaxy along several position angles, in order to estimate the uncertainty in deriving the central gradient of the total mass density from long-slit spectroscopy. We report the detection of strong non-ordered motions of the ionized gas in three out of four sample galaxies. The deviations have velocity amplitudes and spatial scales that make not possible to disentangle between cuspy and core density radial profiles.
