Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.mso.anu.edu.au/~fbriggs/WAARNEEM/dwarfs.PS Дата изменения: Mon Oct 1 22:58:24 2001 Дата индексирования: Tue Oct 2 03:00:41 2012 Кодировка: Поисковые слова: dwingeloo 1

Netherlands Foundation for Research in Astronomy
Stichting Astronomisch Onderzoek in Nederland
NFRA
ASTRON
Radiosterrenwacht Dwingeloo (NFRA/ASTRON)
Postbus 2 Phone +31 521 595100
7990 AA DWINGELOO Fax +31 521 597332
The Netherlands E-mail @nfra.nl
URL http://www.nfra.nl
Bezoekadres: Oude Hoogeveensedijk 4, Dwingeloo
Radiosterrenwacht Westerbork (WSRT)
Schattenberg 1 Phone +31 521 595100
9433 TA ZWIGGELTE Fax +31 593 592486
The Netherlands E-mail @nfra.nl
APPLICATION FOR OBSERVING TIME AT WESTERBORK SEMESTER: 02A
(Please read the instructions before lling in the form)
3. Short title (10 words maximum) of proposed programme
Dimmest HI Dwarf Galaxies
4. Abstract (Concise summary of the proposal)
WSRT observations of two of the dimmest, HI-selected dwarf galaxies SS47 and SS73 will provide reliable coordinates,
as well as a rst look at their sizes and kinematical structure. The observations will complement our imaging program
with Gemini-North. The ultimate goal is to increase the condence in the meaurements of space density for these
illusive LSB galaxies.
Figures: 3
1. Name of principal investigator and mailing address 2. Co-investigators (name & institute code & email)
F.H. Briggs
Kapteyn Inst
Postbus 800
9700 AV Groningen
NL
Email: fbriggs@astro.rug.nl
Phone: 050-3634077
E. Tolstoy (RuG, etolstoy@astro.rug.nl)
5. Total number of hours requested this semester, including calibration:
26
6. Indicate special scheduling requirements (e.g. splitting of observing time, telescope sequence)
7. Indicate whether the investigators will be present at Westerbork at the time of the observations

Yes No
8. For long term projects it is mandatory to indicate here the number of hours of observing time awarded
in previous semesters for this project and the numbers of hours to be requested in future semesters
a) hours awarded in previous b) hours requested this c) hours to be requested
semesters semester in future semesters
0 26 0

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9. Level of support
None  Consultation Extensive Help
10. Summary of required instrumentation
Proposal can be implemented with minimal DZB spectrometer capability: 2 polarizations with 128 channels, Hanning
smoothing, and 1.25 MHz bandwidth. If a greater number of channels or multiple crates of DZB are available, then
higher spectral resolution and wider coverage will be used.
11. Report on the last observations conducted at Westerbork
A) Proposal number:
B) Observing dates: 15-April-2001
C) Results:
Paper in press, A&A: \Did VV 29 collide with a dark Dark-Matter halo? "
12. Applicant's publications related to the subject of this application during the past two years
13. If this programme is for thesis work, indicate:
{ The name of the student:
{ Name of Supervisor:
{ The status of the work:
Starting
In mid-course Near completion
{ Are the data required for completion of the thesis: Yes No
14. Special remarks

{ 3 {
15. Scientic justication of the proposed programme (only gures and tables will be accepted as attachments).
(1 page, continue in box 15 if necessary)
The nature and number density of the lowest mass galaxies is controversial, and astronomers have been unable to
reach agreement on the faint ends of either the optical luminosity function or the HI mass function (HiMF). In fact,
many believe that dim, gas-rich galaxies may dominate the neutral gas content of the Universe, forming a reservoir
of gas-rich building blocks for ongoing accretion and continued star formation in large disk galaxies.
To address the nature of these objects, we are studying three extreme examples (see Fig. 1) of tiny HI-selected
objects from an Arecibo blind 21cm survey by Spitzak and Schneider 1998. In Schneider etals' (1998) analysis of
their sample of 75 galaxies, these three objects are responsible for the divergent tail of the HiMF in Fig. 2.
Figure 1. Optical images and HI spectra for 3 of the dimmest HI selected galaxies, SS47, SS73 and SS75 (Spitzak
& Schneider 1998). Panels are 3 0 3 0 , with the spectra drawn on a velocity scale spanning 1000 km s 1 . Heliocentric
velocities are 563, 469 and 411 km s 1 ; velocity widths at 20% of maximum are 66, 53 and 51 km s 1 ; and HI masses
are 3.9, 1.5 and 0.710 7 M respectively.
Figure 2. The HI Mass Function of Schneider, Spitzak & Rosenberg 1998). The abrupt kink upward at the lowest
masses is due entirely to the three galaxies shown in Fig. 1.
We have been awarded time with Gemini-North to image two of the objects this fall (SS47 and SS73). The
third object is too close to a bright star for useful optical imaging (See Fig 3, next page). The goal of the Gemini
observations to assess the stellar populations and resolve the tip of the giant branch, thereby obtaining an independent
distance determination.
Accurate distances for the objects are crucial in determining the HiMF for these objects, since both the mass
bin that the objects fall into and the `volume correction factors' used for computing number densities depend steeply
on their distances. In blind surveys, these lowest masses can only be detected at small distances, making the use of
Hubble ow velocities vulnerable to peculiar velocity osets.
In fact, these objects fall well o the Tully-Fisher relation when Hubble distances are used. If the Hubble
distances are true, SS47 and SS73 are not only extreme in HI to optically luminosity ratio (MHI =L from 5 to 8),
but also extreme in Dark Matter to baryonic mass ratio. If nudged to greater distance so that they agree with the
T-F relation of other samples of dim, late-type galaxies, the divergent tail of the HiMF in Fig.2 disappears, since the
galaxies would then have greater HI mass and also smaller volume correction factors. Either way, they are fascinating
objects in their own right.
The Goals of these Proposed WSRT Observations are to rene the positions of these objects and make
a rough determination of their angular size and kinematics. These measurements are necessary to the interpretation
of the optical imaging (with a 5 arcmin eld).

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16. Technical requirements for the proposed programme (1 page).
(Continue scientic justication here if necessary)
ARC
SEC
ARC SEC
150 100 50 0 ­50 ­100
200
150
100
50
0
SP­90
Cont peak flux = 1.8855E­02 JY/BEAM
Levs = 1.0000E­03 * ( ­6.00, 6.000, 9.000,
12.00, 15.00, 18.00)
DECLINATION
(B1950)
RIGHT ASCENSION (B1950)
02 54 45 44 43 42 41 40 39
23 36 00
35 45
30
15
00
34 45
30
SS75 WSRT Map SS75 VLA-B Map
Figure 3. SS 75: Preliminary WSRT map (left) with + marking original Arecibo position, and VLA B-array map
(right) (from Briggs and de Bruyn `unpublished archives'). The WSRT map shown here is the rst map made during
the science commissioning of the DZB spectrometer, and it was adequate to demonstrate the Arecibo coordinates are
in error by more than an arcminute; the true position is so close to a 12th magnitude star that an LSB galaxy would
not be identiable in most optical images.
The science goals can be met with one 12 hour observation of each galaxy SS47 and SS73. Since the objects are at
declination 23 ф , the WSRT beam is elongated (13 00 33 00 ), and the full u-v coverage is needed to maximize the north-
south resolution. With spectral coverage of 1.25 MHz (250 km s 1 ) at velocity resolution 4 km s 1 after hanning
smoothing, the observations will reach noise levels of 0:5 mJy/beam/channel (depending a little on taper), while
the peak ux densities in the single dish spectra are 25 mJy. Therefore, we expect to have ample signal-to-noise
ratio to resolve the objects, as would occur if they have structure in the east-west direction. The column density
sensitivity will be 10 19 H-atom cm 2 , allowing for the detection of faint extended HI at column densities well below
the star formation threshold and below the nominal \Damped Lyman-" limit. These objects therefore will add to
the sample available for evaluating interception cross sections for comparison with QSO absorption line studies, at
column densities corresponding to the upper end of the \Lyman limit" QSO absorption line class.
If the Nominal DZB capability is available at the time of the observation, we will expand the velocity coverage
and increase the spectral resolution over that available with only one IF of the DZB (as we have assumed above).
In addition to the 12hours requested per galaxy, we have allocated one hour per object for gain and passband
calibration.
References
Schneider, S.E., & Spitzak, J.G., & Rosenberg, J.I. 1998, ApJ, 507, 9.
Spitzak, J.G. & Schneider, S.E. 1998, ApJS, 119, 159.
Zwaan, M., Briggs, F.H., Sprayberry, D., & Sorar, E. 1997, ApJ, 490, 173

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17. List of sources proposed in this programme:
Object  ф Epoch HA start HA end Freq Vel. or z Spacing 9a[,9b,9c,9d]
h:m:s.s d:m:s.s h:m:s h:m:s Mhz km/s meters
SS47 01:33:51.3 23:33:56 1950 -6:0:0 6:0:0 1417.74 0.001878 Not Critical
SS73 02:45:46.7 23:03:45 1950 -6:0:0 6:0:0 1418.19 0.001564 "
18. Line Transition Specications:
 Frequency: Line Transition: HI21cm Rest Frequency: 1420.4057 MHz
 Velocity: Denition: opt Reference: hel
19. Observation mode: Line
DZB
Observation parameters:
 waveband = 21
 number of polarizations = 2
 backend used = DZB
 number of channels = 128
 bandwidth = 1.25 MHz
 frequency taper = Hanning
 number of bits = 2
 sample integration time = 20 seconds
20. Output Specications:
 Data format: UVFITS
 Data medium: CDROM