# MJD calculation

I was attempting to find a simple way to calculate Modified Julian Day (MJD) from local observing time without having to re-invent the wheel. Someone MUST have done this before. Enter Astropy to save the day. Below is 4 lines of code that’ll do the conversion for you (note I’m using the Ureka installation of python). This was taken from this post on github.

### Host Galaxy Properties

Colour and K-corrections were applied assuming a composite quasar spectrum (Francis et al. 1991) for the nucleus and an elliptical-type SED for the host. Doing this you can measure the absolute magnitude of the host galaxy, the following figure is made:

Absolute magnitude vs. redshift. Green triangles come from a separate study of 100 quasars by HST for comparison.

Controversial topic: relationship between the nucleus and host galaxy luminosity
Assuming quasars emit in a relatively narrow range of Eddington ratio, and that the BH mass is correlated with the mass of the galaxy one would expect to find a correlation between nucleus and host galaxy luminosity. however they do not. they find no significant correlation between the two quantities.

Comparison of the host luminosity vs. nucleus luminosity. The blue line refers to the loci of fixed ratio of 1, 2.5, and 6.25 (i.e., the same, 1 mag, 2 mag).

Morphology
Do quasars inhabit both disc and bulge dominated galaxies? When HST came online, it was able to show that quasars are in both ellipticals and spirals. Stating the morphology of a host galaxy is very difficult, even with the above analysis ‘resolving’ the nucleus from the host. In order to classify the galaxies, the author’s used the value of the Sersic model from the best fits done above. They also redid all the fits as if the galaxy was an elliptical, and all as if the galaxy was a disk. This, however, can only do a preliminary indication, since BOTH components can be present. So they tempered this with visual inspection of all possible available data: images, contour plots, fit of brightness profile, ellipticity following Nair & Abraham (2010) to classify the morphological type. Results:
113 dominated by bulge component
129 dominated by disk structure
64 exhibited mixed bulge+disk equally
100 exhibited complex features
More detailed analysis of the quasars host galaxy morphology is in forthcoming paper.

### Black Hole Mass vs. Host Galaxy Relationship

Black hole masses correlate with: stellar velocity dispersion, the luminosity of host galaxy, mass of spheroidal component. The author’s investigated these relationships for low redshift quasars. The author’s investigate these claims at low redshift. The BH mass is taken from Shen et al. (2011, see section 3.7), who measured the virial mass from H\beta /luminosity relationships.

Black hole mass vs. absolute magnitude of host galaxy

See no correlation really, argue this is because the ‘abs mag of host galaxy’ includes both spheroidals, disks, and disk+spheroidals. Check any redshift dependence?

sees to be no evolution from redshift 0.2 to 0.5

BH mass vs. absolute magnitude of the bulge component of the host galaxy only. This is also supported by the 25 lowest redshift quasars in the sample who’s BH mass is measured via reverberation mapping

### Summary

The authors investigated 416 galaxies that host quasars in Stripe 82. Using a 2D image analysis they were able to well resolve the quasar from the host fro approximately 75% of the sample; selected findings:
1. Morphology of the host galaxies turned out to be rather complex with both bulge and disk dominated galaxies, about one third of the objects in sample show both bulge/disk components.
2. Irrespective of host morphology the size of galaxy ranges from compact to extended (3-15 kpc). no trend of galaxy size with redshift is mentioned.
3. Nuclear and host galaxy luminosities do not correlate
4. BH mass (from H\beta considerations) poorly correlates with total luminosity/mass of WHOLE host galaxy, but correlates with the bulge luminosity, though not particularly strongly.