The compact group--fossil group connection: observations of a massive compact group at z=0.22

It has been suggested that fossil groups could be the cannibalized remains of compact groups, that lost energy through tidal friction. However, in the nearby universe, compact groups which are close to the merging phase and display a wealth of interacting features (such as HCG 31 and HCG 79) have very low velocity dispersions and poor neighborhoods, unlike the massive, cluster-like fossil groups studied to date. In fact, known z=0 compact groups are very seldom embedded in massive enough structures which may have resembled the intergalactic medium of fossil groups. In this paper we study the dynamical properties of CG6, a massive compact group at z=0.220 that has several properties in common with known fossil groups. We report on new g' and i' imaging and multi-slit spectroscopic performed with GMOS on Gemini South. The system has 20 members, within a radius of 1 h_70^-1 Mpc, a velocity dispersion of 700 km/s and has a mass of 1.8 x 10^14 h_70^-1 Msun, similar to that of the most massive fossil groups known. The merging of the four central galaxies in this group would form a galaxy with magnitude M_r' ~ -23.4, typical for first-ranked galaxies of fossil groups. Although nearby compact groups with similar properties to CG 6 are rare, we speculate that such systems occurred more frequently in the past and they may have been the precursors of fossil groups.Comment: 7 pages, 3 figures (one color, low resolution), uses emulateapj.sty. Accepted for publication in ApJ Lette

Intra-group Light in Hickson Compact Groups

We have analyzed the intra-group light component of 3 Hickson Compact Groups (HCG 79, HCG 88 and HCG 95) with detections in two of them: HCG 79, with $46\pm11$ of the total $B$ band luminosity and HCG 95 with $11\pm26$. HCG 88 had no component detected. This component is presumably due to tidally stripped stellar material trapped in the group potential and represents an efficient tool to determine the stage of dynamical evolution and to map its gravitational potential. To detect this low surface brightness structure we have applied the wavelet technique OV\_WAV, which separates the different components of the image according to their spatial characteristic sizes.Comment: Small update on the associated institutions lis

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.Comment: 14 pages, 7 Figures. accepted by A

An optical and X-ray study of the fossil group RX J1340.6+4018

Fossil groups are systems with one single central elliptical galaxy and an unusual lack of luminous galaxies in the inner regions. The standard explanation for the formation of these systems suggests that the lack of bright galaxies is due to galactic cannibalism. In this study we show the results of an optical and X-ray analysis of RX J1340.6+4018, the prototype fossil group. The data indicates that RX J1340.6+4018 is similar to clusters in almost every sense, dynamical mass, X-ray luminosity, M/L and luminosity function, except for the lack of L* galaxies. There are claims in the literature that fossil systems have a lack of small mass haloes, compared to predictions based on the LCDM scenario. The observational data gathered on this and other fossil groups so far offer no support to this idea. Analysis of the SN Ia/SN II ejecta ratio in the inner and outer regions shows a marginally significant central dominance of SN Ia material. This suggests that either the merger which originated the central galaxy was dry or the group has been formed at early epochs, although better data are needed to confirm this result.Comment: Accepted by AJ; 14 pages, 6 figure

Globular Clusters around Galaxies in Groups

We have obtained deep photometry of NGC 1199 (in HCG 22) and NGC 6868 (in the Telescopium group). Both galaxies are the optically brightest galaxies of their groups. Our analysis of B and R images taken with the Keck II and the VLT/ESO telescopes, detected a population of globular clusters around both galaxies, with total specific frequencies S_N=1.7\pm0.6 for NGC 1199 and S_N = 1.3\pm0.6 for NGC 6868. The color distributions of the globular cluster systems shows bimodal peaks centered at (B-R)_0 = 1.13\pm0.10 and 1.42\pm0.10 (NGC 1199) and (B-R)_0=1.12\pm0.10 and 1.42\pm0.10 (NGC 6868).Comment: 3 pages, 1 figure. To appear in the proceedings of IAU Symp. 207, "Extragalactic Star Clusters", eds. E. Grebel, D. Geisler, D. Minnit

Velocity dispersion, mass and the luminosity function of the fossil cluster RX J1416.4+2315

We study the properties of the fossil cluster RX J1416.4+2315 through g' and i'-band imaging and spectroscopy of 25 member galaxies. The system is at a mean redshift of 0.137 and has a velocity dispersion of 584 km s^-1. Superimposed onto one quadrant of the cluster field there is a group of five galaxies at a mean redshift of 0.131, which, if included as part of the cluster, increases the velocity dispersion to 846 km/s. The central object of RX J1416.4+2315 is a normal elliptical galaxy, with no cD envelope. The luminosity function of the system, estimated by the number counts, and statistical background correction, in the range -22.6< M_g'< -16.6, is well fitted by a Schechter function with M_g'^* = -21.2 +/- 0.8 and alpha = -1.2 +/- 0.2 (H_0 = 70 km s^-1 Mpc^-1, Omega_M=0.3, Omega_Lambda=0.7). The luminosity function obtained from the spectroscopically confirmed members in both g' and i' bands agrees with the photometric results. The mass of the system, M 0.9 \times 10^14 h^-1_70 M_sun, its M/L of 445 h_70 M_sun/L_B_sun and L_X of 11 10^43 h^-2_70 ergs s^-1 (bolometric) suggest that this system is the second example of known fossil cluster, after RX J1552.2+2013, confirmed in the literature.Comment: Accepted by AJ - 14 pages, 6 figure

The K luminosity-metallicity relation for dwarf galaxies and the tidal dwarf galaxies in the tails of HCG 31

We determine a K-band luminosity-metallicity (K-Z) relation for dwarf irregular galaxies, over a large range of magnitudes, -20.5 < M_K < -13.5, using a combination of K photometry from either the 2-micron all sky survey (2MASS) or the recent study of Vadivescu er al. (2005), and metallicities derived mainly with the T_e method, from several different studies. We then use this newly-derived relation, together with published K_s photometry and our new spectra of objects in the field of HCG 31 to discuss the nature of the possible tidal dwarf galaxies of this group. We catalogue a new member of HCG 31, namely "R", situated ~40 kpc north of the group center, composed by a ring of H alpha knots which coincides with a peak in HI. This object is a deviant point in the K-Z relation (it has too high metallicity for its luminosity) and its projected distance to the parent galaxy and large gas reservoir makes it one of the most promising tidal dwarf galaxy candidates of HCG 31, together with object F. The subsystems A1, E, F, H and R all have metallicities similar to that of the galaxies A+C and B, result that is expected in a scenario where those were formed from material expelled from the central galaxies of HCG 31. While objects A1, E and H will most probably fall back onto their progenitors, F and R may survive as tidal dwarf galaxies. We find that two galaxies of HCG 31, G and Q, have A+em spectral signatures, and are probably evolving toward a post-starburst phase.Comment: 32 pages, 4 figures - Submitted to AJ - A version of this paper with full resolution figures can be found at http://www.astro.iag.usp.br/~eduardo/HCG31-KZrelation.pd

Photoinduced intersubband transition in undoped HgCdTe multiple quantum wells

We present photoinduced intersubband absorption measurements in HgCdTe undoped quantum wells. The transition energies and the linewidths are well described by a full 8×8 k⋅p Kane model calculation. Also, based on this model we show that different in‐plane effective masses for the first and second electron subbands should be considered in order to properly fit the low energy side of the experimental spectra. The experimental results can be explained using the calculated intersubband oscillator strength with no exciton enhancement. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69671/2/APPLAB-66-22-2998-1.pd

Formation of S0s in extreme environments I: clues from kinematics and stellar populations

Despite numerous efforts, it is still unclear whether lenticular galaxies (S0s) evolve from spirals whose star formation was suppressed, or formed trough mergers or disk instabilities. In this paper we present a pilot study of 21 S0 galaxies in extreme environments (field and cluster), and compare their spatially-resolved kinematics and global stellar populations. Our aim is to identify whether there are different mechanisms that form S0s in different environments. Our results show that the kinematics of S0 galaxies in field and cluster are, indeed, different. Lenticulars in the cluster are more rotationally supported, suggesting that they are formed through processes that involve the rapid consumption or removal of gas (e.g. starvation, ram pressure stripping). In contrast, S0s in the field are more pressure supported, suggesting that minor mergers served mostly to shape their kinematic properties. These results are independent of total mass, luminosity, or disk-to-bulge ratio. On the other hand, the mass-weighted age, metallicity, and star formation time-scale of the galaxies correlate more with mass than with environment, in agreement with known relations from previous work such as the one between mass and metallicity. Overall, our results re-enforce the idea that there are multiple mechanisms that produce S0s, and that both mass and environment play key roles. A larger sample is highly desirable to confirm or refute the results and the interpretation of this pilot study