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Joanna Kuraszkiewicz

Publications and source records attributed to Joanna Kuraszkiewicz.

23 records · Page 2Linked to original sources

The Spectral Energy Distributions of Red 2MASS AGN

We present infrared (IR) to X-ray spectral energy distributions (SEDs) for 44 red AGN selected from the 2MASS survey on the basis of their red J-K$_S$ color (>2 mag) and later observed by Chandra. In comparison with optically-, radio-, and X-ray selected AGN, their median SEDs are red in the optical and near-IR with little/no blue bump. It thus seems that near-IR color selection isolates the reddest subset of AGN that can be classified optically. The shape of the SEDs is generally consistent with modest absorption by gas (in the X-ray) and dust (in the optical-IR). The levels of obscuration, estimated from X-rays, far-IR and our detailed optical/near-IR color modeling are all consistent implying N_H < few*10^{22} cm^{-2}. We present SED models that show how the AGN optical/near-IR colors change due to differing amounts of reddening, AGN to host galaxy ratio, redshift and scattered light emission and apply them to the sources in the sample. We find that the 2MASS AGN optical color, B-R, and to a lesser extent the near-IR color, J-K$_S$, are strongly affected by reddening, host galaxy emission, redshift, and in few, highly polarized objects, also by scattered AGN light. The obscuration/inclination of the AGN allows us to see weaker emission components which are generally swamped by the AGN.

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PCA of the spectral energy distribution and emission line properties of red 2MASS AGN

We analyze the spectral energy distributions (SEDs) and emission line properties of the red (J-K$_S$ > 2) 2MASS AGN observed by Chandra using principle component analysis. The sample includes 44 low redshift AGN with low or moderate obscuration (N_H < 10^{23} cm^{-2}) as indicated by X-rays and SED modeling. The obscuration of the AGN allows us to see weaker emission components (host galaxy emission, AGN scattered light) which are usually outshone by the AGN. The first four eigenvectors explain 70% of the variance in the sample. The dominant cause of variance in the sample (eigenvector 1) is the L/Ledd ratio strengthened by intrinsic absorption. Eigenvector 2 is related to host galaxy (relative to the observed AGN) emission and eigenvectors 3 and 4 distinguish between two sources of obscuration: host galaxy absorption and circumnuclear absorption. Although our analysis is consistent with unification schemes where inclination dependent obscuration is important in determining the AGN SEDs, the L/Ledd ratio is the most important factor, followed by host galaxy emission.

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Probing the Central Engine of the Narrow-Line Seyfert 1 Galaxies

The central engine of the the Narrow Line Seyfert 1 galaxies is being probed. We use the ASCA and RXTE data to model the X-ray primary continuum as well as the reflected component and iron $Kα$ line. Since these are strongly coupled, we obtain independent measurements of the disc ionization level and the orientation dependent reflection amplitude. Using the available Optical/UV data we also estimate the black hole masses and the $L/L_{Edd}$ ratios, which are probably related to Boroson & Green eigenvector~1.

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Evolution of Active Galaxies: Black-hole Mass - Bulge relations for Narrow Line Objects

Mathur (2000) has proposed that the narrow line Seyfert 1 galaxies (NLS1s) are likely to be the active galaxies in early stage of evolution. To test this hypothesis, we have calculated the black hole (BH) masses and the host galaxy bulge masses for a sample of NLS1s. We find that the mean BH to bulge mass ratio of NLS1s is significantly smaller than that for normal Seyfert galaxies. We also find that the ratio of BH mass to bulge velocity dispersion is also significantly smaller for NLS1s. A scenario of BH growth is our preferred interpretation, though alternative explanations are discussed. Assuming that the BHs grow with accretion with a radiative efficiency of 0.1, it will take them about $3.3\times 10^8$ years to become as massive as in normal Seyfert 1s. These timescales are consistent with the theoretical estimates of quasar timescale $t_Q$ less than about $4.5\times 10^8$ years calculated by Haehnelt, Natarajan & Rees (1998). Studies of low redshift NLS1s thus provide a powerful, and due to their proximity relatively easy, way to understand the high redshift quasars and their evolution.

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Quasar Evolution and the Baldwin Effect in the Large Bright Quasar Survey

From a large homogeneous sample of optical/UV emission line measurements for 993 quasars from the Large Bright Quasar Survey (LBQS), we study correlations between emission line equivalent width and both restframe ultraviolet luminosity (i.e., the Baldwin Effect) and redshift. Our semi-automated spectral fitting accounts for absorption lines, fits blended iron emission, and provides upper limits to weak emission lines. Use of a single large, well-defined sample and consistent emission line measurements allows us to sensitively detect many correlations, most of which have been previously noted. A new finding is a significant Baldwin Effect in UV iron emission. Further analysis reveals that the primary correlation of iron emission strength is probably with redshift, implying an evolutionary rather than a luminosity effect. We show that for most emission lines with a significant Baldwin Effect, and for some without, evolution dominates over luminosity effects. This may reflect evolution in abundances, in cloud covering factors, or overall cloud conditions such as density and ionization. We find that in our sample, a putative correlation between Baldwin Effect slope and the ionization potential is not significant. Uniform measurements of other large quasar samples will extend the luminosity and redshift range of such spectral studies and provide even stronger tests of spectral evolution.

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