Using data from the Wide-field Infrared Survey Explorer (WISE) we show that the mid infrared (MIR) colors of low-luminosity AGNs (LLAGNs) are significanlty different from those of post-asymptotic giant branch stars (PAGBs). This is due to a differenc
e in spectral energy distribution (SEDs), the LLAGNs showing a flat component due to an AGN. Consistent with this interpretation we show that in a MIR color-color diagram the LINERs and the Seyfert~2s follow a power law with specific colors that allow to distinguish them from each other, and from star forming galaxies, according to their present level of star formation. Based on this result we present a new diagnostic diagram in the MIR that confirms the classification obtained in the optical using standard diagnostic diagrams, clearly identifying LINERs and LLAGNs as genuine AGNs.
Using a sample of 229618 narrow emission-line galaxies, we have determined the normal star formation histories (SFHs) for galaxies with different activity types: star forming galaxies (SFGs), transition type objects (TOs), Seyfert 2s (Sy2s) and LINER
s. We find that the variation of the SFH with the activity type is explained by the mass of the galaxies and the importance of their bulge: the LINERs reside in massive early-type galaxies, the Sy2s and TOs are hosted by intermediate mass galaxies with intermediate morphological types, and the SFGs are found in lower mass late-type spirals. Except for the Sy2s, the more massive galaxies formed the bulk of their stars more rapidly than the less massive ones. The Sy2s formed their stars more slowly and show presently an excess in star formation. We have also found that the maximum in star formation rate in the past increases with the virial mass within the aperture (VMA), the VMA increasing from the SFGs to the TOs, to the Sy2s, culminating in the LINERs. This correlation suggests that the bulges and the supermassive black holes at the center of galaxies grow in parallel, in good agreement with the M(BH)-sigma relation.
The broad MgII doublet has been much studied in connection with its potentially important role as a virial estimator of black hole mass in high redshift quasars. An important task is therefore identification of any line components likely related to b
roadening by non-virial motions. High s/n median composite spectra (binned in the 4D eigenvector 1 context of Sulentic et al. 2007) were constructed for the brightest 680 SDSS DR7 quasars in the 0.4 < z < 0.75 range where both MgII 2800 and Hbeta are recorded in the same spectra. Composite spectra representing 90% of the quasars confirm previous findings that FWHM(MgII 2800) is about 20% narrower than FWHM(Hbeta). The situation is clearly different for the most extreme (Population A) sources which are the highest Eddington radiators in the sample. In the median spectra of these sources FWHM MgII 2800 is equal to or greater than FWHM(Hbeta) and shows a significant blueshift relative to Hbeta. We interpret the MgII 2800 blueshift as the signature of a radiation-driven wind or outflow in the highest accreting quasars. In this interpretation the MgII 2800 line width -- affected by blueshifted emission -- is unsuitable for virial mass estimation in ~ 10% of quasars.
We discuss the nature and origin of the nuclear activity observed in a sample of 292 SDSS narrow-emission-line galaxies, considered to have formed and evolved in isolation. All these galaxies are spiral like and show some kind of nuclear activity. Th
e fraction of Narrow Line AGNs (NLAGNs) and Transition type Objects (TOs; a NLAGN with circumnuclear star formation) is relatively high, amounting to 64% of the galaxies. There is a definite trend for the NLAGNs to appear in early-type spirals, while the star forming galaxies and TOs are found in later-type spirals. We verify that the probability for a galaxy to show an AGN characteristic increases with the bulge mass of the galaxy (Torre-Papaqui et al. 2011), and find evidence that this trend is really a by-product of the morphology, suggesting that the AGN phenomenon is intimately connected with the formation process of the galaxies. Consistent with this interpretation, we establish a strong connection between the astration rate--the efficiency with which the gas is transformed into stars--the AGN phenomenon, and the gravitational binding energy of the galaxies: the higher the binding energy, the higher the astration rate and the higher the probability to find an AGN. The NLAGNs in our sample are consistent with scaled-down or powered-dow
In this second paper of two analyses, we present near-infrared (NIR) morphological and asymmetry studies performed in sample of 92 galaxies found in different density environments: galaxies in Compact Groups (HCGs), Isolated Pairs of Galaxies (KPGs),
and Isolated Galaxies (KIGs). Both studies have proved useful for identifying the effect of interactions on galaxies. In the NIR, the properties of the galaxies in HCGs, KPGs, and KIGs are more similar than they are in the optical. This is because the NIR band traces the older stellar populations, which formed earlier and are more relaxed than the younger populations. However, we found asymmetries related to interactions in both KPG and HCG samples. In HCGs, the fraction of asymmetric galaxies is even higher than what we found in the optical. In the KPGs the interactions look like very recent events, while in the HCGs galaxies are more morphologically evolved and show properties suggesting they suffered more frequent interactions. The key difference seems to be the absence of star formation in the HCGs; while interactions produce intense star formation in the KPGs, we do not see this effect in the HCGs. This is consistent with the dry merger hypothesis (Coziol & Plauchu-Frayn 2007); the interaction between galaxies in compact groups, (CGs), is happening without the presence of gas. If the gas was spent in stellar formation (to build the bulge of the numerous early-type galaxies), then the HCGs possibly started interacting sometime before the KPGs. On the other hand, the dry interaction condition in CGs suggests that the galaxies are on merging orbits, and consequently such system cannot be that much older either. [abridge]
