HDLT Deep Imaging of the LITTLE THINGS Galaxies

Background

The LITTLE THINGS Survey was granted close to 376 hours of time with the VLA in the B, C, and D array configurations 2007-2008 to obtain deep HI-line maps of dwarf galaxies. The purpose is to determine how tiny galaxies form stars. We observed 21 dwarf irregular (dIm) and Blue Compact Dwarf (BCD) galaxies, and are adding another 20 dwarfs with data in the VLA Archives. The new observations consist of 12 hours in B-array, 6 hours in C-array, and 2 hours in D-array for each galaxy. The channel separation is 2.6 km/s for 31 galaxies and 1.3 km/s for 11 galaxies.

The combined B/C/D arrays sample the galaxies at 6 arcseconds, which is 110 pc at 3.7 Mpc, the average distance of our sample. This resolution shows clouds, shells, and turbulent structures that are important for star formation. We also produce maps at lower resolution that reveal the extended, low-density gas around star formation structures and trace the low density HI far beyond the stellar disks.

A paper, Martinez-Delgado, D., et al. (2009). "Discovery of a Giant Stellar Tidal Stream Around the Disk Galaxy NGC 4013." The Astrophysical Journal, 692, 955-963, indicated that discovery of stellar tidal streams can be done with a rather modest telescope. In this case, the galaxy was obseved for many hours but with numerous exposures. The images were then added to produce the required exposure time.

Discovery of tidal streams around the LITTLE THINGS galaxies would provide extremely valuable insights into the star forming processes at play in these galaxies.

Image Requirements

The images for this project need to meet the following requirements:

  Surface Brightness (mag/arcsec2)
Telescope
Aperture (m)
28.0 28.5 29.0 29.5 30.0
0.2 15.1 37.8 95.0 238.6 599.4
0.3 6.7 16.8 42.2 106.1 266.4
0.4 3.8 9.5 23.7 59.7 149.9
0.5 2.4 6.1 15.2 38.2 95.9
0.6 1.7 4.2 10.6 26.5 66.6
0.7 1.2 3.1 7.8 19.5 48.9
0.8 0.9 2.4 5.9 14.9 37.5
0.9 0.7 1.9 4.7 11.8 29.6
1.0 0.6 1.5 3.8 9.5 24.0

Exposure time (h) required to reach the indicated surface brightness.

The table indicates small telescopes require hundreds of hours and are, therefore, unsuitable for this project.

Because a single filter was not used for the reference data, one might expect slighly different times in single filter operation. A telescope with a low f/ratio (like f/2) might require less time.

Management

There may be more than one amateur astronomer involved in this effort. In order to avoid duplicated effort, each amateur should have an assigned galaxy to observe. Of course we will select the galaxies that provide the maximum observing time each night consistent with local observing conditions.

When the image is "complete" we will evaluate it and decide if we require more time on the object. If not, we will move to another galaxy. There are 41 galaxies in the LITTLE THINGS program so there should be plenty of work.

Targets

The following table lists all of the LITTLE THINGS galaxies in RA order with their J2000 coordinates, their approximate size at B = 25 mag and their apparent magnitude (with bandpass, where available).

NameRADec.Apparent
Dimensions
(B=25)
Apparent
Mag
WLM00 01 56.9-15 27 0111.48′ x 3.98′11.3
IC 1000 20 24.6+59 17 306.31′ x 5.13′11.8 B
LGS 301 03 56.6+21 53 411.20′ x 0.70′14.2
IC 161301 04 48.4+02 07 1016.22′ x 14.45′9.88
NGC 115602 59 42.6+25 14 153.31′ x 2.45′12.32
NGC 156904 30 50.3+64 50 473.63′ x 1.79′11.86
DDO 4307 28 17.3+40 46 141.32′ x 0.82′15.7
NGC 236607 28 54.4+69 12 528.13′ x 3.31′11.43
DDO 4607 41 24.0+40 06 001.74′ x 1.70′13.9
DDO 4707 41 54.0+16 48 003.09′ x 2.95′13.6
DDO 5008 19 06.0+70 42 517.94′ x 2.95′11.10
M81dwA08 23 56.0+71 01 461.30′ x 1.20′16.5
DDO 5208 28 24.0+41 51 002.46′ x 1.26′15.0
DDO 5308 34 06.0+66 10 001.55′ x 1.35′14.48
F564-V309 02 54.0+20 04 270.55′ x 0.55′18.35
NGC 373809 04 00.2+21 58 051.44′ x 0.62′12.13
DDO 6309 40 24.0+71 11 003.63′ x 2.95′13.0
DDO 6909 59 18.0+30 44 005.25′ x 3.16′12.92
DDO 7009 59 59.9+05 19 575.13′ x 3.55′11.85
DDO 7510 11 01.3-04 42 485.89′ x 4.90′11.86
DDO 8710 49 36.0+65 31 002.40′ x 2.40′15.1
VIIZw 40311 28 00.0+78 59 001.44′ x 0.32′14.5
Mrk 17811 33 28.5+49 14 081.23′ x 0.66′-
DDO 10111 55 36.0+31 30 002.90′ x 1.29′14.80
NGC 416312 12 09.1+36 10 101.82′ x 1.62′14.5
NGC 421412 15 39.5+36 19 398.52′ x 6.61′10.24
Haro 2912 26 16.1+48 29 310.83′ x 0.60′15.15
DDO 12612 27 05.2+37 08 343.16′ x 1.99′14.2
DDO 13312 32 48.0+31 32 006.46′ x 4.47′13.0
CVnIdwA12 38 40.0+32 46 001.00′ x 0.70′16.00
Haro 3612 46 56.3+51 36 491.29′ x 1.00′14.1g
DDO 15412 54 05.3+27 09 133.02′ x 2.19′13.94
DDO 15512 58 36.0+14 13 001.07′ x 1.02′14.68
DDO 16513 06 26.9+67 42 153.47′ x 1.90′12.8
DDO 16713 13 18.0+46 19 001.12′ x 0.62′17.
DDO 16813 14 28.6+45 55 103.63′ x 1.38′12.7
UGC 850813 30 42.0+54 54 001.70′ x 1.02′14.4
DDO 18714 15 54.0+23 03 001.66′ x 1.29′14.38
NGC 682219 44 57.9-14 48 1115.49′ x 13.49′09.31
SagDIG19 29 59.6-17 40 422.88′ x 2.14′14.1B
DDO 21020 46 51.8-12 50 532.24′ x 1.15′14.0B
DDO 21623 28 34.1+14 44 485.01′ x 2.69′13.21
   Clark Telescope

Lowell's 24-inch Alvan Clark refracting telescope