VLASS – Galactic Science

Life cycle of star formation in our Galaxy as a proxy for understanding the Local

Universe legacy science

Infrared GLIMPSE survey

VLASS – Galactic ScienceDetailed study and Identification of High Mass Star

Formation Regions

• high mass stars have a huge effect on their environs, through UV radiation, wind energy, shocks, enriching the ISM

• our understanding of high mass star formation is woefully incomplete: triggered star formation vs. spontaneous collapse?

• these stars drive winds and jets, which are compact thermal sources

• H II regions form once the star has contracted down to the main sequence, and are useful probes of high mass star formation

• methanol masers are associated with regions of high mass star formation

HST image of NGC 3603, showing a cluster of massive star formation

GLIMPSE and CORNISH (5 GHz survey)

VLASS – Galactic Science

Detection of a previously unknown planetary nebula from the CORNISH survey, Hoare et al. (2012). Left: 5 GHz Middle: Spitzer GLIMPSE (3.6,4.5,8 um) Right: UKIDSS (JHK)

Stellar Winds, Planetary Nebulae, and Active Stars

• thermal radio emission from stellar winds complements UV, optical studies• evolved OB stars reside in the densest part of the Galaxy• understanding mass loss mass and energy flows in local Universe

• PN have flat radio spectra in the GHz range (methanol masers reveal physical conditions)• only 3000 (of proposed 23,000) planetary nebula currently known (Frew & Parker 2010)• rates of detection and mass loss rates affect models for input energy into ISM

• Magnetically active stars have flat radio spectra from non-thermal emission with possible gyroresonance at higher frequencies; high spatial resolution enables identification

VLASS – Galactic ScienceSetting the Landscape

Ku band survey is complementary with many other survey efforts

VLASS – Galactic Scienceexample: constraining thermal sources

Typical spectral energy distribution of an Ultra-Compact HII region (red curve). The distinctive shape is the product of two emission processes: thermal radiation from warm dust (the 'hump') and thermal free-free radio emission from ionised gas (the 'plateau'). Fluxes normalized

With the proposed sensitivity,radio emission can be used to distinguish between these typesof thermal sources in star formingregions Hoare et al. (2012)

radio loud UCHII regions radio quiet Massive YSOs

CORNISH limited in scope! sensitivity and spatial coverage

VLASS – Galactic Science• Key Science Advantages of Ku band

– sensitivity is optimized to thermal sources (a > +0.6)– access to 12.2 GHz methanol maser (usually associated with 6.7 GHz methanol

maser and star formation) to help constrain pumping mechanism; access to recombination lines

– complementary with infrared and submillimeter surveys that trace dusty regions of early and current star formation

– picks up thermal emission from dense plasmas which are missed by lower frequencies

• Key Science Disadvantages of S band– baseline sensitivity of 30 mJy will not pick up the same population as the

baseline sensitivity at Ku band will: miss many optically thick, thermal sources! – non-thermal (AGN) contamination will make source identification nature very

difficult at S-band– no spectral lines (methanol maser very important indicator of star forming

regions; recombination lines provide basic kinematics)

VLASS – Galactic Science

Parameters of Proposed Survey

Galactic Latitude Coverage