Minutes of the 2nd Sunday Afternoon Discussion

Reconvening after the coffee break

Wim	There seems to be a consensus that there should be a shallow survey. We might also suggest that we set up subcommittees so that the survey specifications can be discussed by the animators of the shallow survey but also possible other surveys. There also seems to be consensus for some deep survey(s), though they will take a long time. We can start by using the surveys discussed by Riccardo as benchmarks. also consider some deeper surveys, e.g., Virgo, ZOA, strip, survey around nearby galaxies (as mentioned by Judith) or whatever. A deep Virgo survey would give us not only Virgo but everything behind it. We should also consider what we would want in a deep strip survey or a deep survey of some selected regions. We certainly want 200 MHz for the deep surveys. The background for most of our discussion is the HIMF.
Brent	I think the single most interesting part of the sky is CanVen w/in 1000 km/s. It happens to be at the same RA as Virgo.
Jon	Why is it more interesting?
Brent	You will find more dwarfs there. There aren't many in Virgo, except in the periphery. While there are lots and lots of dI's in Virgo, it's not the richest part of the sky dI's.
Jon	You need to look in different regions in order to study different mechanisms for stripping. Is it tidal? Is it hot gas?
Brent	Yes, I am all in favor of that, but let's also look at richest region, the one most likely to have lots and lots of dwarfs.
Jon	But non-detections are also interesting, because they allow us to place limits.
Peppo	Can you remind us of what CanVen is like?
Brent	It's not a cluster. There are 2 features separated in redshift, CVnI and CVnII. Declination 30 to 40.
Peppo	Is there any X-ray emission from the gas?
Brent	I doubt it. These are very low mass groups, and the region contains only a couple of big galaxies. And, the biggest galaxies are not very big. To survey this, you need to cover at least 100 square degrees.
Wim	We have recently done a blind survey of the Can Ven region with Nancay.
Jon	But would this really be a survey or just another Arecibo application?
Noah	How about a Right Ascension strip not a declination strip?
Riccardo	That would really not be practical with Arecibo because of its semi-transit nature. It would be very expensive in terms of telescope time.
Wim	Jon asked a good question: Is this more of a big survey or just an application?
Liese vZ	The CVn dwarf UA 292 has the 2nd lowest (known) metallicity. So that a survey of this region might be interesting to probe an environment that is known to be immensely gas rich.
Riccardo	For a shallow survey such as the Virgo one I described, 100 square degrees only needs 100 hours. That's not a big deal.
Wim	So, this might be considered a single application, like the large galaxy project.
Liese	What Judith is proposing is a big survey also.
Brent	I would want to go very deep. There are two groups, one at 5 Mpc and the other at 10 Mpc.
Riccardo	You'd need about 100 hours for to cover 100 square degrees to a limit of 106.8 solar masses at 10 Mpc. If you want to go to 106 solar masses, you are talking big time.
Karen O.	Let's talk a little about Judith's idea.
Judith	What we already know is that if there is HI gas, then there is star formation. But how are the two connected? That's what's interesting to CDM models. We would like to know what the environment around isolated objects is like, for example, looking for HVC's, determining the sizes of HI disks. To do this with any resolution, you have to restrict the sample to large galaxies, probably within 10 Mpc.
Wim	Why large angular size?
Judith	You would want enough information to determine the size scale of the HI distribution and perhaps measure very outer rotation curve points. So you want the galaxies certainly to be bigger than the Arecibo beam. For example, you could look at the UGC galaxies > 5 arcmin that are found in the AO declination range. There are about 100 of them. Maybe you want to survey around the biggest/nearest 25. We need to work the numbers a bit here.
DJ P.	You want to go out a couple of 100 kpc around these galaxies to look for HVCs.
Wim	This might be the kind of project that lends itself to a pilot survey.
Lyle H.	Are we going to be able to deal with the beam pattern?
Wim	GALFA will be fussier about this than we will.
Karen O.	We hope so. This is where we need to worry about what we need in order to clean our maps, then we tell NAIC what we need to know in order to do it.
Steve S.	The VLA will be doing a survey of Virgo galaxies and another of large galaxies.
Karen O.	At this point, we can have several groups to hash out details of (a) shallow survey and (b) deep surveys.
Peppo	Can we come back to Virgo again. Remember than in the same region, in the background, we sample the bridge between Coma and A1367. This bridge has a low velocity dispersion. So, it is a great place to look for HI rich galaxies, but because of the larger distance, to do that, we need some sensitivity. Another point is that there is a void in the foreground. A nice idea is a narrow vertical strip.
Wim	It becomes a matter of priorities. What about the ZOA survey?
Liese	Do we get this one for free?
Karen O.	We should decide first what we want for the science.
Jim C.	You would not get the whole 10 degrees.
Trish H.	What is always the driver in ZOA surveys is to map the large scale structure behind the ZOA. So I would argue for a shorter time because we are really looking only locally. Also, you need to watch were the obscuration is. 10 degrees might be overkill.
Riccardo	The 300 seconds was dictated by the concept that this would be done in piggyback.
Steve	That's for their .
Karen O.	How deep should we go?
Jim	Perhaps we'd go with 60 seconds out to (or ).
Trish	The survey strategy will be important, because you need positional accuracy. So I think the best would be drift scans.
DJ	So is 60 seconds plenty of time for that?
Trish	Yes.
Wim	So, really let's set up some subcommittees to look into the surveys. shallow survey:     RG & Lister deep survey:        Karen O. ZOA survey:        Trish
Riccardo	What is the charge to the subcommittee?
Wim	The point is: what is expected at the end of this meeting is to produce as precise-as-possible a document that expresses our wishes with respect to NAIC. So we need a group to lay out the requirements for h/w & s/w, write text on what does this survey mean scientifically, technically, and especially with respect to NAIC.
Karen O.	We need to know where we might look for deep survey, and what are the survey parameters, so that I can present them to the GALFA workshop later in the week.
Steve	Are you expecting a report at the end of day tomorrow with science objective/motivation and specification of survey in as much detail as possible?
Karen O.	Yes. So each subcommittee needs to come up with a draft, and then present it to the whole group for discussion tomorrow.
DJ	Did we come to a consensus as to which survey the "Nearby Galaxy Project" belongs or even whether it belongs to one of the main surveys or to its own?
Karen O.	It belongs to the "deep" project but may also be individual too
Wim	Let's get back to the list of potential discussion topics
Karen O.	The issue of 100 or 200 MHz needs to be discussed after the survey meetings
Steve	I think there is a sense that we might want to do things a little differently. Rather than breaking up into groups, we might want to discuss all together. Could I volunteer Lister and Riccardo to summarize what they think has been discussed today?
Jon	Yes, let those two guys come with a summary for the rest of us to discuss tomorrow.
Lister	There is some discussion of deep surveys but could they be clarified?
Wim	There is no consensus on a deep survey.
Lister	How many deep surveys are there?
Karen O.	1. Virgo 200 - 810 square deg 60 sec or 240 sec over limited 2. Can Ven 100 square deg   3. Around big galaxies 100 square deg   4. Really deep field 2 - 5 square deg few thousand seconds per beam 5. Deep declination strip 360 square deg   6. ZOA   piggyback?
Liese	How much sky would be surveyed around each galaxy?
Mary	That would depend on the distance to the galaxy.
Liese	So can't we just call this a "1000 square degree deep survey"?
Riccardo	What is integration time for such a survey?
Karen O.	We might want to do these surveys all with same depth.
Steve	Let me throw some numbers out: solar masses at 10 Mpc for narrow line for 60 sec/beam.
Jon	Given the extension of Virgo along line of sight, it would be nice to go deeper. If we integrated 240 sec/beam, then we could sample the whole depth of the cluster. You will be incomplete in the last mass bin, so you only actually get to solar masses. You could reduce the area by 4 and increase the time by 4.
Liese	If the big galaxies are at 10 Mpc, you don't need the same integration time as for Virgo.
Karen O.	But, if you want to be able to combine deep surveys, it would be nice to have same time for everything.
Lister	Surely there is also a need for a really deep survey for distant objects, one that integrates per pointing say hundreds or even thousands of secs.
Jon	What is the scientific motivation for such a survey?
Lister	Galaxy evolution even at quite low redshifts, say cz = 0.1, in clusters.
Jon	Can you make a study of the evolution of the HI mass fraction? Can you actually do something like that?
Noah	I question going deep with an instrument that doesn't have very high spatial resolution.
Karen O.	It has better resolution than any other single dish telescope.
Eli	While the spatial resolution is limited, but redshift spread might help.
Jon	You need the optical counterparts to measure the HI content.
Steve	I think in that time you are going to detect Virgo survey. So why do you want thousands of seconds. How deep do you need to go?
Lister	We ought to go to solar masses, well below M* for the HIMF.
Brent	You will never find an object at solar masses without an optical counterpart.
DJ	There are lots of optical surveys that might suggest where are the interesting places to study the B-O effect.
Steve	Lister is interested in looking for evolution of the HIMF.
Brent	Looking for evolution of the HIMF is a great idea, but I don't think you'll solve it with 2 square degrees.
Riccardo	What is difference of this versus AHISS?
Karen O.	It would go to higher velocities.
Ed S.	I am strongly against number 4. It would be a mistake to think that we'll learn about evolution from HI.
Lister	I have not worked this out carefully, but the only instrument that can do this today is Arecibo. Arecibo with ALFA could probe what the SKA might actually learn.
Riccardo	Note that the ZOA survey if it were done in piggyback with the pulsar survey would have 300 sec.
Lister	I am not sure that the way data are taken will get you to the theoretical noise level. The array will have rotated between on and off.
Jon	I think we really need to carve out a niche for what ALFA does that HIPASS did not do. I think that evolution is really important.
Karen O.	I suggest that Lister and Jon take a look at numbers over night.
Wim	We also need to prioritize if we are going to put 3000 hours on the table.
Karen O.	What about the ZOA survey?
Brent	Are we assuming it is done in piggybacking?
Trish	We have to worry about strategy and whether it is worth it or not. I am not sure we can afford to piggyback because we need to be sure of positional accuracy. So we need to know what the tolerances on the pulsar survey are.
Jim	I think you need to decide what you really need to do the science.
Trish	Something like M* at Coma.
Steve	But that is easy.
Jim	We'd be interested in 60-120 seconds to higher latitude.
Trish	That would probably work.
Steve	So we need to Nyquist sample so that we can get positional accuracy.
Jim	It also important that we get the telescope time.

Discussion of Backends

Wim	Let's talk about backends and whether we need 100 or 200 MHz. It may be that it's technically not possible, but let's look at the main science arguments first.
Phil P.	Remember that the 200 MHz option could also be used to double your resolution over 100 MHz.
Steve	Are the WAPPs completely tunable?
Karen O.	They are separate, with a gap in between them, but Bill says he could put an LO in to allow them to overlap.
Steve	Can you drop to 50 MHz to do what Phil is suggesting?
Karen O.	Yes.
DJ	Better resolution would be good for rfi excision.
Desh	Would there be any interest in looking for OH in the upper band? (Apparently not in this group.)
Karen O.	It seems like a waste not to sample. You get solar masses for free.
Noah	I would agree with your position for reasons of large scale structure. An HI survey is a completely different sampling than the IR surveys.
Lister	The shallow surveys will be bandpass limited at 100 MHz It might be a little awkward to do a survey with rfi.
Karen O.	I have done lots of contiguous bandwidth observations with not much interference I found galaxies out to 1290 or to 1250 MHz. It doesn't kill the entire band. You lose a few MHz here and there.
Trish	Do we want to make a statement regarding internal RFI?
Murray	Yes, I think you should make a statement about your needs.

Discussion of Proprietary Rights