arXiv subjects

Dalya Baron

Publications and source records attributed to Dalya Baron.

39 records · Page 3Linked to original sources

arXiv2016

Evidence that most type 1 AGN are reddened by dust in the host ISM

The typical optical-UV continuum slopes observed in many type 1 AGN are redder than expected from thin accretion disk models. A possible resolution to this conundrum is that many AGN are reddened by dust along the line of sight. To explore this possibility, we stack 5000 SDSS AGN with luminosity L~10^45erg/s and redshift z~0.4 in bins of optical continuum slope alpha_opt and width of the broad H$β$ emission line. We measure the EW of the NaID absorption feature in each stacked spectrum. We find a linear relation between alpha_opt and EW(NaID), such that EW(NaID) increases as alpha_opt becomes redder. In the bin with the smallest H$β$ width, objects with the bluest slopes that are similar to accretion disk predictions are found to have EW(NaID)=0, supporting the line-of-sight dust hypothesis. This conclusion is also supported by the dependence of the $Hα/Hβ$ line ratio on alpha_opt. The implied relationship between alpha_opt and dust reddening is given by E(B-V)~0.2(-0.1-alpha_opt), and the implied reddening of a typical type 1 AGN with alpha_opt=-0.5 is E(B-V)~0.08mag. Photoionization calculations show that the dusty gas responsible for reddening is too ionized to produce the observed features. Therefore, we argue that the sodium absorption arises in regions of the host ISM which are shielded from the AGN radiation, and the correlation with alpha_opt arises since ISM columns along shielded and non-shielded sightlines are correlated. This scenario is supported by the similarity of the E(B-V)-NaID relation implied by our results with the relation in the Milky-Way found by previous studies.

astro-ph.GA↗

arXiv2015

Using machine learning to classify the diffuse interstellar bands

Using over a million and a half extragalactic spectra we study the correlations of the Diffuse Interstellar Bands (DIBs) in the Milky Way. We measure the correlation between DIB strength and dust extinction for 142 DIBs using 24 stacked spectra in the reddening range E(B-V) < 0.2, many more lines than ever studied before. Most of the DIBs do not correlate with dust extinction. However, we find 10 weak and barely studied DIBs with correlations that are higher than 0.7 with dust extinction and confirm the high correlation of additional 5 strong DIBs. Furthermore, we find a pair of DIBs, 5925.9A and 5927.5A which exhibits significant negative correlation with dust extinction, indicating that their carrier may be depleted on dust. We use Machine Learning algorithms to divide the DIBs to spectroscopic families based on 250 stacked spectra. By removing the dust dependency we study how DIBs follow their local environment. We thus obtain 6 groups of weak DIBs, 4 of which are tightly associated with C2 or CN absorption lines.

astro-ph.GA↗

arXiv2014

Dusting off the diffuse interstellar bands: DIBs and dust in extragalactic SDSS spectra

Using over a million and a half extragalactic spectra we study the properties of the mysterious Diffuse Interstellar Bands (DIBs) in the Milky Way. These data provide us with an unprecedented sampling of the skies at high Galactic-latitude and low dust-column-density. We present our method, study the correlation of the equivalent width of 8 DIBs with dust extinction and with a few atomic species, and the distribution of four DIBs - 5780.6A, 5797.1A, 6204.3A, and 6613.6A - over nearly 15000 squared degrees. As previously found, DIBs strengths correlate with extinction and therefore inevitably with each other. However, we show that DIBs can exist even in dust free areas. Furthermore, we find that the DIBs correlation with dust varies significantly over the sky. DIB under- or over-densities, relative to the expectation from dust, are often spread over hundreds of square degrees. These patches are different for the four DIBs, showing that they are unlikely to originate from the same carrier, as previously suggested.

astro-ph.GA↗