Sowgat Muzahid

Search for cold gas in strong Mg II absorbers at 0.5 < z < 1.5: nature and evolution of 21-cm absorbers

We report 4 new detections of 21-cm absorption from a systematic search of 21-cm absorption in a sample of 17 strong (Wr(MgII 2796)>1A) intervening MgII absorbers at 0.5 100 km/s are mainly seen towards the quasars with extended radio morphology at arcsecond scales. However, we do not find any correlation between the integrated 21-cm optical depth or DeltaV with the LS measured from the milliarcsecond scale images. All this can be understood if the absorbing gas is patchy with a typical correlation length of ~30-100 pc. We show that within the measurement uncertainty, the 21-cm detection rate in strong MgII systems is constant over 0.5<z<1.5, i.e., over ~30% of the total age of universe. We show that the detection rate can be underestimated by up to a factor 2 if 21-cm optical depths are not corrected for the partial coverage estimated using milliarcsecond scale maps. Since stellar feedback processes are expected to diminish the filling factor of cold neutral medium over 0.5<z<1, this lack of evolution in the 21-cm detection rate in strong MgII absorbers is intriguing. [abridged]

THE AZIMUTHAL DEPENDENCE OF OUTFLOWS AND ACCRETION DETECTED USING O vi ABSORPTION

We report a bimodality in the azimuthal angle (

An HST/COS survey of molecular hydrogen in DLAs & sub-DLAs at z < 1: molecular fraction and excitation temperature

\Phi

HST/COS detection of a Ne viii absorber towards PG 1407+265: an unambiguous tracer of collisionally ionized hot gas?

) distribution of gas around galaxies traced by OVI absorption. We present the mean

21-cm absorption from galaxies at z ~ 0.3

\Phi

HST/COS observations of a new population of associated QSO absorbers

probability distribution function of 29 HST-imaged OVI absorbing (EW>0.1A) and 24~non-absorbing (EW<0.1A) isolated galaxies (0.08<z<0.67) within 200kpc of background quasars. We show that EW is anti-correlated with impact parameter and OVI covering fraction decreases from 80% within 50kpc to 33% at 200kpc. The presence of OVI absorption is azimuthally dependent and occurs between

Molecular hydrogen absorption from the Halo of A z ~ 0.4 Galaxy

\pm10-20^{\circ}

A pair of O vi and broad Ly α absorbers probing warm gas in a galaxy group environment at z ∼ 0.4

of the galaxy projected major axis and within

Cold parsec-scale gas in a zabs ∼ 0.1 sub-damped Lyman α with disparate H2 and 21-cm absorption

\pm30^{\circ}

Revisiting the He ii to H i ratio in the intergalactic medium

of the projected minor axis. We find higher EWs along the projected minor axis with weaker EWs along the project major axis. Highly inclined galaxies have the lowest covering fractions due to minimized outflow/inflow cross-section geometry. Absorbing galaxies also have bluer colors while non-absorbers have redder colors, suggesting that star-formation is a key driver in the OVI detection rate. OVI surrounding blue galaxies exists primarily along the projected minor axis with wide opening angles while OVI surrounding red galaxies exists primarily along the projected major axis with smaller opening angles, which may explain why absorption around red galaxies is less frequently detected. Our results are consistent with CGM originating from major axis-fed inflows/recycled gas and from minor axis-driven outflows. Non-detected OVI occurs between