2017, Bell, Eric, Monachesi, Antonela, D’Souza, Richard, Harmsen, Benjamin, de Jong, Roelof, Radburn-Smith, David, Bailin, Jeremy, Holwerda, Benne

Galaxy mergers are expected to influence galaxy properties, yet measurements of individual merger histories are lacking. Models predict that merger histories can be measured using stellar halos and that these halos can be quantified using observations of resolved stars along their minor axis. Such observations reveal that Milky Way-mass galaxies have a wide range of stellar halo properties and show a correlation between their stellar halo masses and metallicities. This correlation agrees with merger-driven models where stellar halos are formed by satellite galaxy disruption. In these models, the largest accreted satellite dominates the stellar halo properties. Consequently, the observed diversity in the stellar halos of MilkyWay-mass galaxies implies a large range in the masses of their largest merger partners. In particular, the Milky Way's low mass halo implies an unusually quiet merger history. We used these measurements to seek predicted correlations between the bulge and central black hole (BH) mass and the mass of the largest merger partner. We found no significant correlations: while some galaxies with large bulges and BHs have large stellar halos and thus experienced a major or minor merger, half have small stellar halos and never experienced a significant merger event. These results indicate that bulge and BH growth is not solely driven by merger-related processes.

2016, Zola, S., Valtonen, M., Bhatta, G., Goyal, A., Debski, B., Baran, A., Krzesinski, J., Siwak, M., Ciprini, S., Gopakumar, A., Jermak, H., Nilsson, K., Reichart, D., Matsumoto, K., Sadakane, K., Gazeas, K., Kidger, M., Piirola, V., Alicavus, F., Baliyan, K., Berdyugin, A., Boyd, D., Campas Torrent, M., Campos, F., Carrillo Gómez, J., Caton, D., Chavushyan, V., Dalessio, J., Dimitrov, D., Drozdz, M., Er, H., Erdem, A., Escartin Pérez, A., Fallah Ramazani, V., Filippenko, A., Garcia, F., Gómez Pinilla, F., Gopinathan, M., Haislip, J., Harmanen, J., Hudec, R., Hurst, G., Ivarsen, K., Jelinek, M., Joshi, A., Kagitani, M., Kaur, N., Keel, W., LaCluyze, A., Lee, B., Lindfors, E., Lozano de Haro, J., Moore, J., Mugrauer, M., Naves Nogues, R., Neely, A., Nelson, R., Ogloza, W., Okano, S., Pandey, J., Perri, M., Pihajoki, P., Poyner, G., Provencal, J., Pursimo, T., Raj, A., Reinthal, R., Sadegi, S., Sakanoi, T., Sameer, null, Salto González, J.-L., Schweyer, T., Soldán Alfaro, F., Karaman, N., Sonbas, E., Steele, I., Stocke, J., Strobl, J., Takalo, L., Tomov, T., Tremosa Espasa, L., Valdes, J., Valero Pérez, J., Verrecchia, F., Webb, J., Yoneda, M., Zejmo, M., Zheng, W., Telting, J., Saario, J., Reynolds, T., Kvammen, A., Gafton, E., Karjalainen, R., Blay, P.

We analyse the light curve in the R band of the blazar OJ287, gathered during the 2015/2016 observing season. We did a search for quasi-periodic oscillations (QPOs) using several methods over a wide range of timescales. No statistically significant periods were found in the high-frequency domain both in the ground-based data and in Kepler observations. In the longer-period domain, the Lomb–Scargle periodogram revealed several peaks above the 99% significance level. The longest one—about 95 days—corresponds to the innermost stable circular orbit (ISCO) period of the more massive black hole. The 43-day period could be an alias, or it can be attributed to accretion in the form of a two-armed spiral wave.

2017, Oman, Kyle, Starkenburg, Else, Navarro, Julio

The stellar halos of galaxies encode their accretion histories. In particular, the median metallicity of a halo is determined primarily by the mass of the most massive accreted object. We use hydrodynamical cosmological simulations from the APOSTLE project to study the connection between the stellar mass, the metallicity distribution, and the stellar age distribution of a halo and the identity of its most massive progenitor. We find that the stellar populations in an accreted halo typically resemble the old stellar populations in a present-day dwarf galaxy with a stellar mass ~0.2-0.5 dex greater than that of the stellar halo. This suggests that had they not been accreted, the primary progenitors of stellar halos would have evolved to resemble typical nearby dwarf irregulars.

2015, Sánchez, Sebastian, Sánchez-Menguiano, Laura, Marino, Raffaella, Rosales-Ortega, F., Pérez, Isabel, de Paz, Armando, Pérez, Enrique, Walcher, C., López-Cobá, Carlos

We present here a review of the latest results on the spatially-resolved analysis of the stellar populations and ionized gas of disk-dominated galaxies based on Calar Alto Legacy Integral Field Area (CALIFA) data. CALIFA is an ongoing integral field spectroscopy (IFS) survey of galaxies in the Local Universe (0.005 < z < 0.03) that has already obtained spectroscopic information up to ∼2.5 re with a spatial resolution better than ∼1 kpc for a total number of more than 600 galaxies of different morphological types, covering the color-magnitude diagram up to MR<−18 mag. With nearly 2000 spectra obtained for each galaxy, CALIFA offers one of the best IFU datasets to study the star formation histories and chemical enrichment of galaxies. In this article, we focus on the main results from the analysis of the oxygen abundances based on the study of ionized gas in H II regions and individual spaxels and their relation to the global properties of galaxies, using an updated/revised dataset with more galaxies and ionized regions. In summary, we have confirmed previous published results indicating that: (1) the M-Z relation does not present a secondary relation to the star formation rate, when the abundance is measured at the effective radius; (2) the oxygen abundance presents a strong correlation with the stellar surface density (∑-Z relation); (3) the oxygen abundance profiles present three well-defined regimes: (i) an overall negative radial gradient between 0.5 and 2 re, with a characteristic slope of αO/H ∼−0.1 dex/re; (ii) a universal flattening beyond >2 re; and (iii) an inner drop at <0.5 re that depends on mass; (4) the presence of bending in the surface brightness profile of disk galaxies is not clearly related to either the change in the shape of the oxygen abundance profile or the properties of the underlying stellar population. All of these results indicate that disk galaxies present an overall inside-out growth, with chemical enrichment and stellar mass growth tightly correlated and dominated by local processes and limited effects of radial mixing or global outflows. However, clear deviations are shown with respect to this simple scenario, which affect the abundance profiles in both the innermost and outermost regions of galaxies

2016, Fan, Junhui, Kurtanidze, Omar, Liu, Yi, Liu, Xiang, Richter, Gotthard, Nikolashvili, Maria, Kurtanidze, Sophia, Chanishvili, Revaz, Wang, Hongtao, Sasada, Mahito, Zhou, Aiying, Lin, Chao, Yuan, Yuhai

In this work, we present optical R band observations of AO 0235+164 carried out during the period of November 2006 to December 2012 using the Ap6E CCD camera attached to the primary focus of the 70 cm meniscus telescope at Abastumani Observatory, Georgia. It shows a large variation of ΔR = 4.88 mag (14.19–19.07 mag) and a short time scale of ΔTv = 73.5 min during our monitoring period. When periodicity analysis methods are applied to the R-band data from both historic and our observations, periods P1 = 8.26 yr and P2 = 0.54 yr are found.