About DGIS

Servey Design

DGIS aims to obtain 3-D (2-D space plus 1-D electromagnetic wavelength) mapping of a volume-limited representative sample of low-mass galaxies. The stellar masses of galaxies range from 1E6 to 1E9 solar mass. Observations are carried out with WiFeS on ANU 2.3 m telescope and MUSE on VLT.

Sample

T he sample in DGIS is representative by including all objects in the Spitzer LVL program with declination (DEC) less than 20 degree, stellar mass lower than 10^9 solar mass, and distance less than 11 Mpc, based on the properties provided in Table 1 of Dale et al. (2009). The final sample is composed of 65 objects, with the Small Magellanic Cloud (SMC) excluded. Their basic properties are summarized The sample covers a distance ranging from 0.44 to 11.4 Mpc, except for two objects located largely beyond 11 Mpc, according to the updated distance data from NED. The stellar masses range from 1e6 solar mass to 1e9 solar mass, with 60% of the sample falling within the 1e8 - 1e9 solar mass range. The sample includes all Hubble types, with a majority of them being dwarf irregulars.

Target Lists

Observation

ANU/WiFeS

WiFeS is an integral field, double-beam, concentric, image-slicing spectrograph mounted on the 2.3 m telescope at Siding Spring Observatory (SSO). The high resolution grisms, including U7000, B7000, R7000, and I7000, are employed to cover the full optical wavelength range from 329 to 912 nm, with a resolution of about 7000. It provides 25 slitlets, each 38" long and 1" wide, offering a FOV of 25" x 38" and a pixel scale of 1" x 0.5". Each source is observed with a single pointing. Each exposure lasts 20 to 30 minutes, followed by an off-target sky exposure of 5 to 10 minutes. A standard star is observed every 1 to 2 hours. Only exposures taken under clear weather conditions are included in the final dataproducts. The final integrated on-source exposure time per spatial pixel per wavelength grid is between 2 and 7 hrs. Among them, the U7000 and R7000 are observed simultaneously with the configuration of RT480, and the B7000 and I7000 are observed simultaneously with the RT615. Spatial binning of 1x2 is applied to a final pixel scale of 1" x 1". WiFeS observations are 80% complete.

VLT/MUSE

MUSE is a second-generation instrument of the VLT. It has 24 integral field units (IFU). In Wide Field Mode (WFM)-NOAO-E mode, it covers the optical wavelength range from 465 to 930 nm with a spectral resolution of 2800 at 6563 AA, a FOV of 60" x 60", and a pixel size of 0.2" x 0.2" (see Bacon et al. 2010, for details). The final datacube has a binned spaxel size of 0.4" x 0.4" and an average seeing of around 0.8". Most sources have a single pointing, except for WLM with 4 pointings, UGC00668 with 9 pointings, and UGC12613 with 3 pointings. The total on-source exposure time per spaxel for most sources ranges from 2200 to 4800 seconds. This time is divided into several exposures, each lasting between 5 and 20 minutes, followed by an off-target sky exposure of around 1 to 2 minutes. So far, MUSE observations are 88% complete.

More Details

DGIS SCIENCE

Cycles between different baryonic components are the driving mechanisms for galaxy formation and evolution: gas collapses into stars, causing star formation processes; stars pollute the ISM by producing metals; the mix of metals and dust with gas regulates cooling efficiency; the CGM freshes the gas reservoir and dilutes the metallicity in galaxies; outflows/radiation from stars and central massive black holes influence the ISM and CGM in various aspects; radial migration and interaction with satellites reshape the morphologies and kinematics of gas and stars. These processes have been extensively studied in massive galaxies, demonstrating that a galaxy is a complicated ecosystem that can only be fully understood by studying all these processes. DGIS will advance studies of dwarf galaxies by enabling measurements of various galactic components, as well as their spatial distribution and kinematics, by combining with its rich ancillary data. Combined with IFU data for massive galaxies available in the literature, DGIS will enable a more complete understanding of the physical processes driving galaxy formation and evolution across a wide stellar mass scale.

Massive black holes born in the early Universe left relics in dwarf galaxies today. Instead of sinking to the galactic center, they could exist across the galaxy given their long dynamical timescale. The population of these IMBHs and their physical properties offer crucial insights into the formation mechanisms of SMBH seeds and their growth. Hunting for these IMBHs has been extremely difficult because (i) their bolometric luminosity is of the same order of magnitude as that of massive evolved stars; (ii) light pollution from ambient stellar emission significantly dilutes the radiation from IMBHs; (iii) searching over the galaxy body is more observationally challenging than those with single-slit/fiber observations. Currently, through various methods, roughly 1% of dwarf galaxies within the stellar mass range of DGIS are found to host active BHs, with almost all of them located at galactic centers. DGIS has been designed to maximize the success of IMBH hunting in dwarfs by covering a significant fraction of the galaxy body (roughly to Re), providing high spatial resolution combined with high S/N to eliminate stellar dilution significantly, and offering multiple diagnostics (BPT diagram, He II, broad emission line) to identify active BH accretion.

While the LambdaCDM has achieved tremendous success in matching the observations at the large scale of the Universe, there are distinct differences at small scales. The inner profile of dark matter is one of them, with core profiles preferred in observations versus cuspy profiles predicted in simulations. Because dwarf galaxies are dominated by dark matter even at their centers, they have been ideal laboratories for understanding the above core/cuspy problem To have a reliable measurement of the inner profile, one needs to probe the kinematics within the central 100 pc, which requires a spatial resolution as small as tens of parsec. As shown in the collections of rotation curves of dwarf galaxies, only a few objects have kinematic measurements within the central 100 pc. Our proposed observations will remedy this situation by in creasing the sample size by a few factors.