NoSOCS in SDSS. VI. The Environmental Dependence of AGN in Clusters and Field in the Local Universe

We investigated the variation in the fraction of optical active galactic nuclei (AGN) hosts with stellar mass, as well as their local and global environments. Our sample is composed of cluster members and field galaxies at $z \le 0.1$ and we consider only strong AGN. We find a strong variation in the AGN fraction ($F_{AGN}$) with stellar mass. The field population comprises a higher AGN fraction compared to the global cluster population, especially for objects with log $M_* > 10.6$. Hence, we restricted our analysis to more massive objects. We detected a smooth variation in the $F_{AGN}$ with local stellar mass density for cluster objects, reaching a plateau in the field environment. As a function of clustercentric distance we verify that $F_{AGN}$ is roughly constant for R $>$ R$_{200}$, but show a steep decline inwards. We have also verified the dependence of the AGN population on cluster velocity dispersion, finding a constant behavior for low mass systems ($\sigma_P \lesssim 650-700$ km s$^{-1}$). However, there is a strong decline in $F_{AGN}$ for higher mass clusters ($>$ 700 km s$^{-1}$). When comparing the $F_{AGN}$ in clusters with or without substructure we only find different results for objects at large radii (R $>$ R$_{200}$), in the sense that clusters with substructure present some excess in the AGN fraction. Finally, we have found that the phase-space distribution of AGN cluster members is significantly different than other populations. Due to the environmental dependence of $F_{AGN}$ and their phase-space distribution we interpret AGN to be the result of galaxy interactions, favored in environments where the relative velocities are low, typical of the field, low mass groups or cluster outskirts.Comment: 11 pages, 10 figures, Accepted to MNRA

Classifying LEP Data with Support Vector Algorithms

We have studied the application of different classification algorithms in the analysis of simulated high energy physics data. Whereas Neural Network algorithms have become a standard tool for data analysis, the performance of other classifiers such as Support Vector Machines has not yet been tested in this environment. We chose two different problems to compare the performance of a Support Vector Machine and a Neural Net trained with back-propagation: tagging events of the type e+e- -> ccbar and the identification of muons produced in multihadronic e+e- annihilation events.Comment: 7 pages, 4 figures, submitted to proceedings of AIHENP99, Crete, April 199

Field galaxies at intermediate redshift (0.2 < z < 0.8) in the direction of the galaxy cluster LCDCS-S001

We present spectroscopic and photometric analysis for eight field galaxies in the direction of the galaxy cluster LCDCS-S001. The spectra were obtained with the GMOS instrument in the Gemini South Observatory. The objects were selected in an i' band image and the multi-object spectroscopic observations were centered at 7500 A. For the galaxies ID 440 and ID 461 we have determined redshifts of z=0.7464 and z=0.7465, respectively. For the other six galaxies we have confirmed the redshift calculated by Rembold & Pastoriza (2006). The redshifts of the field galaxies are in the range of 0.2201 < z < 0.7784. We determined the blue and visual luminosities and they are brighter than M_B=-18.64. The galaxies ID 180, ID 266, ID 461 follow the Faber-Jackson relation of the Coma and Virgo early-type galaxies, and therefore do not present a brightening of the B luminosity as observed in galaxies at higher redshifts. The stellar velocity dispersion was measured for five galaxies and estimated to be in the range of 200 < sigma < 346 km/s. Lick indices were measured and used to determine the stellar population properties of galaxies ID 120 and ID 146, by means of spectral synthesis. The first galaxy, ID 120, presents in its spectrum absorption and emission lines, and we have found that the main contribution in the flux at lambda 5870 A is of a 0.1 Gyr stellar population of solar metallicity. For ID 146, the dominant flux contribution at lambda 4200 A, is provided by a stellar population of 10 Gyr of subsolar metallicity. From stellar population synthesis we estimated reddening values of E(B-V)=0.90 and E(B-V)=0.82 for ID 120 and ID 146, respectively. According to classical diagnostic diagrams the emission lines present in the spectrum of ID 120 indicate that it is a starburst galaxy.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical. 6 Figures and 4 table

Probing Stellar Populations and Interstellar Medium in Early-Type Central Galaxies

In this study, we analyse the characteristics of stellar populations and the interstellar medium (ISM) in 15,107 early-type central galaxies from the SPIDER survey. Using optical spectra from the Sloan Digital Sky Survey (SDSS), we investigate stellar age (Age), metallicity ($Z$), visual extinction ($A_{\rm V}$), and H$\alpha$ equivalent width (EWH$\alpha$) to understand the evolution of the baryonic content in these galaxies. Our analysis explores the relationship between these properties and central velocity dispersion ($\sigma$) and halo mass ($M_{\rm halo}$) for isolated centrals (ICs) and group centrals (GCs). Our results confirm that both ICs and GCs' stellar populations and gas properties are mainly influenced by $\sigma$, with $M_{\rm halo}$ playing a secondary role. Higher $\sigma$ values correspond to older, more metal-rich stellar populations in both ICs and GCs. Moreover, fixed $\sigma$ values we observe younger Ages at higher values of $M_{\rm halo}$, a consistent trend in both ICs and GCs. Furthermore, we investigate the ionisation source of the warm gas and propose a scenario where the properties of ionised gas are shaped by a combination of cooling within the intra-cluster medium (ICM) and feedback from Active Galactic Nuclei (AGN) assuming a Bondi accretion regime. We observe inherent differences between ICs and GCs, suggesting that the ratio between AGN kinetic power and ICM thermal energy influences EWH$\alpha$ in ICs. Meanwhile, gas deposition in GCs appears to involve a more complex interplay beyond a singular AGN-ICM interaction.Comment: 14 pages, 11 figures, accepted for publication in the MNRA

Morphology of AGN Emission Line Regions in SDSS-IV MaNGA Survey

Extended narrow-line regions (NLRs) around active galactic nuclei (AGN) are shaped by the distribution of gas in the host galaxy and by the geometry of the circumnuclear obscuration, and thus they can be used to test the AGN unification model. In this work, we quantify the morphologies of the narrow-line regions in 308 nearby AGNs ($z=0-0.14$, \lbol $\sim 10^{42.4-44.1}$ \erg{}) from the MaNGA survey. Based on the narrow-line region maps, we find that a large fraction (81\%) of these AGN have bi-conical NLR morphology. The distribution of their measured opening angles suggests that the intrinsic opening angles of the ionization cones has a mean value of 85--98$^\circ$ with a finite spread of 39-44$^\circ$ (1-$\sigma$). Our inferred opening angle distribution implies a number ratio of type I to type II AGN of 1:1.6--2.3, consistent with other measurements of the type I / type II ratio at low AGN luminosities. Combining these measurements with the WISE photometry data, we find that redder mid-IR color (lower effective temperature of dust) corresponds to stronger and narrower photo-ionized bicones. This relation is in agreement with the unification model that suggests that the bi-conical narrow-line regions are shaped by a toroidal dusty structure within a few pc from the AGN. Furthermore, we find a significant alignment between the minor axis of host galaxy disks and AGN ionization cones. Together, these findings suggest that obscuration on both circumnuclear ($\sim$pc) and galactic ($\sim$ kpc) scales are important in shaping and orienting the AGN narrow-line regions.Comment: 14 pages, 7 figures, and 1 table, accepted for publication in MNRA