MALT90 Parameters

Summary Table

Number of dense cores observed 2,000
Number of Pre-stellar cores 700
Number of Protostellar cores 500
Number of HII Region cores 600
Number of PDR cores 200
Angular Resolution 38 arcsec
Spectral Resolution 0.11 km/s
Lines mapped simultaneously 16
Size of each map 3 arcmin x 3 arcmin
Sensitivity (TA x rms at 0.11 km/s) 0.2 K
Total Survey size 1.2+ TBytes
Time for one map 1.18 hours
Total time for survey 2800 hours
Survey Region +20° > l > +3° and -3° > l > -60°
Complete to cores with M > 200 Msun 7 kpc
Dates of data collection Austral winter 2010-2013

Lines observed

IFLine Frequency (MHz)Tracer
1N2H+(1-0) 93,173.480Density, chemically robust
213CS (2-1) 92,494.303Column density
3H41α 92,034.475Ionized gas
4CH3CN 5(1)-4(1) 91,985.316Hot core
5HC3N (10-9) 91,199.796Hot core
613C34 S(2-1) 90,926.036Column density
7HNC (1-0) 90,663.572Density; cold chemistry
8HC13CCN (10-9) 90,593.059Hot core
9HCO+ (1-0) 89,188.526Density
10HCN (1-0) 88,631.847Density
11HNCO (41,3 - 31,2) 88,239.027Hot core
12HNCO (40,4-30,3) 87,925.238Hot core
13C2H (1-0) 87,316.925Photodissociation tracer
14HN13C (1-0) 87,090.85Column density
15SiO (2-1) 86,847.010Shock/outflow tracer
16H13CO+ (1-0) 86,754.330Column density

Classification Scheme

Although ATLASGAL is an excellent finding chart for dense cores, it contains a heterogeneous mix of warm and cold cores spanning a wide range of masses. In order to adequately sample high-mass star-forming dense cores in both the cold pre-stellar phase and the warm protostellar and HII region phases, it is necessary to classify the evolutionary state of the star-formation activity taking place within the cores. Fortunately, the Spitzer infrared surveys GLIMPSE and MIPSGAL allows one to separate the cores into the various evolutionary states. We use these surveys to categorize the cores into four groups.

Pre-stellar

Since these are cold and very dense, pre-stellar cores will be infrared dark in the GLIMPSE 3.6 to 8.0 µm and MIPSGAL 24 µm images.

GLIMPSE 3.6, 4.5 and 8.0 µm image GLIMPSE 3.6, 8.0 µm/MIPSGAL 24 µm

Protostellar

Accretion onto a protostar is signalled by warm dust. Thus, an embedded 24 µm point source in MIPSGAL with no GLIMPSE emission indicates an embedded, accreting protostar. An additional sign is the presence of extended 4.5 µm emission, the characteristic "green fuzzy".

GLIMPSE 3.6, 4.5 and 8.0 µm image GLIMPSE 3.6, 8.0 µm/MIPSGAL 24 µm

HII Region

When the HII region forms, the surrounding gas and dust are heated and the infrared emission associated with the core will be bright in both GLIMPSE and MIPSGAL images. The morphologies of HII regions range from compact, to extended, with some displaying bubble-like morphologies.

GLIMPSE 3.6, 4.5 and 8.0 µm image GLIMPSE 3.6, 8.0 µm/MIPSGAL 24 µm

Photodissociation Region (PDR)

The UV radiation from a recently formed high-mass star will produce a photodissociation region (PDR) at the molecular/ionised gas interface. The PDR will be extended and emit strongly in the GLIMPSE 8 um images. Moreover, extended 24 um emission indicative of hot dust will also be present. PDRs will have extended morphologies.

GLIMPSE 3.6, 4.5 and 8.0 µm image GLIMPSE 3.6, 8.0 µm/MIPSGAL 24 µm