Galaxies on Top of Quasars: Probing Dwarf Galaxies in the Sloan Digital Sky

Survey

Lorrie Straka

D. York, P. Noterdaeme, R. Srianand, D. Bowen, P. Khare, M. Bishof, Z. Whichard, V. Kulkarni

AAS: Probes of Dark Matter on Galaxy ScalesMonterey, CAJuly 16, 2013

Outline

Quasar absorption line systems (QSOALS) – a review

Current issues in QSOALS Galaxies on Top of Quasars (GOTOQs) Results Dwarf and dark galaxy connections Future studies

Quasar Absorption Line Systems

Absorption systems have been studied for decades for their unique insight into galaxy properties

– QSOALS eliminate luminosity bias in galaxy selection Detection in emission has been challenging

– Imaging and emission spectroscopy necessary to understand the environments of these systems

Lyα and Mg II

– UV observations

– DLA (log N(HI) > 20.3) Optical features: Ca II and Na I

QSOALS

Pettini 2004

QSOALS – Current Questions

How are these absorption features related to their environments?

– Morphology, mass, SFR How are absorption properties related to emission

properties in the same system? Where are all the dwarf galaxies? How are dark galaxies related? A sample of low-z quasar-galaxy pairs detected in

emission can help make a connection with higher-z QSOALS

Galaxies on Top of Quasars

Low-z galaxies intervening with background quasars in the SDSS

– Narrow galactic emission lines in SDSS QSO spectra

Strong galactic emission lines present in QSO spectra indicate a part of a galaxy falling within 3” of the line of sight

– Spectral fiber 3” in diameter

GOTOQs

Automated searches for nine strong galactic emission lines

– Hα; Hβ; [O II] λ3727; [O III] λλ4959,5008; [N II] λλ6550,6585; [S II] λλ6718,6733

These galaxies are ideal targets for studying:

– The relationship between absorption and emission properties

– Environment along line of sight to QSO

– Provides a sample of dwarf and dark galaxies

GOTOQ Search Results

• All of SDSS DR7 QSO spectra searched

– 104,374 QSO spectra searched

– 635 systems flagged as potential GOTOQs

– About 120 confirmed as positive results

• Galaxies are primarily late type with low SFR

– (u-r) colors solidly in late type range with a few green valley candidates

• E(B-V) values show higher reddening than Mg II selected samples (York et al. 2006)

• ~30% of sample: no detected absorption

Results

• ~50% of our sample are dwarf galaxies by L*<0.2, with a further 15% having 0.2 < L*<0.4

• >50% of our sample have SFR < 1 Msolar

yr-1

• 17% have no detections in imaging (but were detected via spectral emission)

– Dark galaxies?

Dwarf Galaxies

• L* < 0.2

• Satellites of more massive galaxies

• Concerning dwarf galaxies:

– “Missing satellites:” theory predicts many more dwarf galaxies than we observe

– Models fail to match the abundance of low stellar mass galaxies at z > 0

• Our search has returned a sizable sample of dwarf galaxies for study in addressing these issues that otherwise may have been missed completely

Dark Galaxies

• Galaxies extremely difficult to detect in IR, optical, or UV due to their low stellar content and suppressed SFR

• Halos that never reach the critical enrichment threshold to become luminous (10-3 Z

solar )

• Mhalo

< 1010 Msolar

• Depletion times > 20 Gyr

– (MHI

+ MH2

)/SFR

Dark Galaxies

• Recent dark galaxy detections include:

– Leo P (Rhode et al. 2013)

– 1225 + 01 (Matsuoka et al. 2012)

• Both detected in the ALFALFA survey with follow up observations in optical

Mat

suo k

a et

al .

(20 1

2 )

Dark Galaxies

• Kuhlen et al. (2013)

– H2 suppression of star formation

– Low metallicity, low SFR, low mass dark halos

– 789/1010 simulated halos dark

z(gal) = 0.357

Current and Future Work

• Integral Field Spectroscopy (IFS)

– “3D” spectroscopy

– Ideal for diffuse objects

• How can IFS help?

– Distribution of gas

– Velocity maps

– Mapping of dark and dwarf galaxies

– Total SFR

– Decoupling of QSO and galaxy light

Current and Future Work

• Radio observations

– HI and CO for clues to star formation suppression and

quenching

• UV observations

– Lyα and Mg II for connections with higher redshift absorption systems

• High resolution imaging

• Mass estimates

• SDSS DR9 search

Summary

• Automated search drastically increases efficiency of finding GOTOQs

– Galaxies may not have otherwise been found

• Database of dwarf and dark galaxies

• Properties of emission and absorption where both are present

• Dark galaxies may play a larger role in QSOALS than previously expected