arXiv subjects

Laerte Sodre Jr

Publications and source records attributed to Laerte Sodre Jr.

3 recordsLinked to original sources

arXiv2012

Cosmology with large redshift surveys

Galaxy redshift surveys are a major tool to address the most challenging cosmological problems facing cosmology, like the nature of dark energy and properties dark matter. The same observations are useful for a much larger variety of scientific applications, from the study of small bodies in the solar system, to properties of tidal streams in the Milky Way halo, to galaxy formation and evolution. Here I briefly discuss what is a redshift survey and how it can be used to attack astrophysical and cosmological problems. I finish with a brief description of a new survey, the Javalambre Physics of the Accelerating Universe Astrophysical Survey (JPAS), which will use an innovative system of 56 filters to map ~8000 square degrees on the sky. JPAS photometric system, besides providing accurate photometric redshifts useful for cosmological parameter estimation, will deliver a low-resolution spectrum at each pixel on the sky, allowing for the first time an almost all-sky IFU science.

astro-ph.CO↗

arXiv2005

The luminosity function of the fossil group RX J1552.2+2013

We determine the first fossil group luminosity function based on spectroscopy of the member galaxies. The fossil group RX J1552.2+2013 has 36 confirmed members, it is at a mean redshift of 0.136 and has a velocity dispersion of 623 km/s (or 797 km/s if four emission lines galaxies in the outskirts of the velocity distribution are included). The luminosity function of RX J1552.2+2013, measured within the inner region of the system ~1/3 R_vir), in the range -23.5< M_i'<-17.5, is well fitted by a Schechter function with M*i'=-21.3 +/- 0.4 and alpha = -0.6 +/- 0.3 or a Gaussian function centered on M_i'= -20.0 +/- 0.4 and with sigma=1.29 +/- 0.24 i' mag. (H_0 = 70 km/s Mpc, Omega_M=0.3, Omega_Lambda=0.7. The luminosity function obtained from a photometric survey in g', r', i'-bands (and statistical background correction) confirms the spectroscopically determined results. There is a significant dip in the luminosity function at M_r'=-18 mag, as also observed for other clusters. RX~J1552.2+2013 is a rich, strongly red-galaxy dominated system, with at least 19 galaxies with magnitudes between m_3 and m_3 + 2, within a surveyed circular area of radius 625 kpc centered on the peak of the x-ray emission. Its mass, ~3.0 10^14 M_0, M/L of 507 M_sol/L_B_sol and L_X of 6.3 10^43 ergs/s (bolometric) are more representative of a fossil cluster than of a fossil group. The central object of RX J1552.2+2013 is a cD galaxy which may have accreted the more luminous ~L* former members of the group. Although dynamical friction and subsequent merging are probably the processes responsible for the lack of bright galaxies in the system, for the fainter members, there must be another mechanism in action (perhaps tidal disruption) to deplete the fossil group from intermediate-luminosity galaxies M_r' ~ -18.

astro-ph↗

arXiv2004

Star formation and the environment of nearby field galaxies

We investigate the environmental dependence of galaxies with star formation from a volume-limited sample of 4782 nearby field galaxy spectra extracted from the 2dF Galaxy Redshift Survey final data release. The environment is characterized by the local spatial density of galaxies, estimated from the distance to the 5th nearest neighbour. Extensive simulations have been made to estimate correction factors for the local density due to sample incompleteness. We discriminate the galaxies in distinct spectral classes -- passive, star-forming, and short starburst galaxies -- by the use of the equivalent widths of [{\sc O ii}]$λ$3727 and H$δ$. The frequency of galaxies of different classes are then evaluated as a function of the environment. We show that the fraction of star-forming galaxies decreases with increasing density, whereas passive galaxies present the opposite behaviour. The fraction of short starburst galaxies -- that suffered a starburst at $\sim$ 200 Myr ago -- do not present strong environmental dependence. The fraction of this class of galaxies is also approximately constant with galaxy luminosity, except for the faintest bins in the sample, where their fraction seems to increase. We find that the star-formation properties are affected in all range of densities present in our sample (that excludes clusters), what supports the idea that star-formation in galaxies is affected by the environment everywhere. We suggest that mechanisms like tidal interactions, which act in all environments, do play a relevant role on the star-formation in galaxies.

astro-ph↗