PROPOSAL FOR 30M TELESCOPE Deadline: 17 Sep 2009 Period: 01 Dec May 2010

Transcription

1 IRAM 3, rue de la Piscine 3846 ST. MARTIN d HERES (France) Fax: (33/) PROPOSAL FOR 3M TELESCOPE Deadline: 17 Sep 29 Period: 1 Dec May 21 Registration N : Date: For IRAM use TITLE A Legacy Survey to Study Cold Gas Scaling Laws in the Local Universe Type: Solar system: continuum lines other Extragalactic: continuum CO lines 2 other Galactic: continuum lines circumstel. env. young stel. obj. cloud struct. chem. other ABSTRACT The scaling laws of galaxies provide a quantitative means of characterizing their physical properties and the route to understanding their formation and evolutionary histories. Current galaxy formation models predict that the scaling relations between the gaseous and stellar components of galaxies provide important information about formation processes (e.g. accretion) occurring at the present day. The study of cold gas scaling laws is currently severely hampered by a lack of suitably large, unbiased samples of galaxies with accurate measurements of total atomic and molecular gas content down to low enough levels to constrain the gas as a reservoir for future galaxy growth. We propose to rectify the situation by obtaining IRAM 3m CO observations for a sample of 3 galaxies uniformly selected from the SDSS spectroscopic and GALEX imaging surveys with deep HI data from Arecibo. We will make this legacy data set available to the entire astronomical community. Is this a resubmission of a previous proposal? no 2 yes proposal number(s): Is this a continuation of (a) previous proposal(s)? no 2 yes proposal number(s): Hours requested for this period: 1 LST range(s): from: to: number of intervals: from: to: number of intervals: Special requirements: Large Program 2 pooled obs 2 service obs remote obs 2 polarimeter Scheduling constraints: Receivers: EMIR 2 HERA Bolometer Other List of Objects (give most common names) Epoch: J2. Source RA DEC V LSR G3261 :55: :46:33. z=.3747 G354 1:18: :37: G3645 1:15: :24: G3777 1:23: :39: G3817 1:43: :51: G3962 2:3: :18: G3971 2:5: :25: G :: :6: G :27: :18: G656 12:43: :34: G725 13:5: :13: G731 13:46: :7: G758 13:5: :11: G :27: :5: G :26: :45: G :33: :38: G :8: :25: G931 14:3: :21: G :16: :37: ( for additional sources which do not fit here use the \extendedsourcelist macro ) Principal Investigator: Guinevere Kauffmann MPA Karl Schwarzschildstr Garching (Germany) Tel: (+49) Fax: (+49) gamk@mpa-garching.mpg.de Other Investigators (name, institution): Carsten Kramer, co-pi (IRAM Spain); C. Buchbender (IRAM Spain); B. Catinella (MPA Germany); L. Cortese (U.Cardiff UK); S. Fabello (MPA Germany); J. Fu (SHAO China); R. Giovanelli (Cornell USA); J. Gracia-Carpio (MPE Germany); Q. Guo (MPA Germany); M. Haynes (Cornell USA); T. Heckman (JHU USA); M. Krumholz (UC Santa Cruz USA); C. Li (MPA Germany); S. Moran (JHU USA); N. Rodriguez-Fernandez (IRAM France); A. Saintonge (University of Zurich Switzerland); D. Schiminovich (Columbia University USA); K. Schuster (IRAM France); A. Sievers (IRAM Spain); L. Tacconi (MPE Germany); J. Wang (MPA Germany); Expected observer(s) see management plan join to this form: scientific aims 2 typed pages ( 4 pages for Large Programs) and 2 pages Figs., Tabs., and Refs.

2 Technical Summary EMIR Note that up to 4 IF signals can be recorded and up to 2 EMIR (always dual polarization) bands can be combined in one EMIR setup. For a summary of EMIR connectivity consult the IRAM Granada home page or the Call for Proposals Transitions = expected line antenna temperature; v = required velocity resolution. T A setup band species transition frequency T A rms v backend a ) GHz mk mk km s 1 E CO W a ) V: VESPA, W: WILMA, 4: 4 MHz filterbank, 1: 1 MHZ filterbank Observing parameters map size in arcmin; T = requested telescope telescope time per setup setup map size mapping switching T remark No. x y mode a ) mode b ) [h] 1 none WSw 55 Total EMIR time requested: 55 a ) none, OTF (on the fly), R: Raster b ) PSw: position switching, FSw: frequency switching, Wsw: wobbler sw. Observing time estimates: (Please read main text first) To estimate the total time required, we estimate molecular gas masses for each of the 21 galaxies in the GASS DR1 sample. Based on our pilot program results, we set M(H 2 ) =.5 M(HI) in cases where the HI line was detected. For non-detections, we assumed that we would need to integrate to the limit of M(H 2 ) =.3 M. We then estimated the CO line peak at the center of the galaxy, taking into account the luminosity distance of the galaxy, the HI line width and the galaxy size. Finally, we used the EMIR/3m observing time estimator to derive the total amount of time required to obtain a 8σ detection in area under average winter/good summer conditions (pwv = 4 mm), an average elevation of 45, and 3 km s channels. (We aim at a velocity resolution of 3 km s, because we would like to compare the CO linewidths with the HI linewidths in a systematic way as part of our scaling relations study). We also estimated the total time to be spent in offset observations assuming I CO(1 ) (offset)/i CO(1 ) (center) =.3 (fig. 5c). The total time (t on + t off ) required to detect the CO line at the central+offset positions (when needed) of the 21 GASS DR1 galaxies was divided by the number of galaxies to estimate the average time per galaxy. This time was multiplied by a factor of 1.5 to include telescope overheads. We consider that this is an appropriate correction (compared to the factor of 2 used in the time estimator) given the rather simple observing strategy described in the proposal. Under these assumptions, we will require on average 1.85 hr (σ = 1.2 mk) to measure the total molecular gas mass of a galaxy. We thus require a total of 55 hr for the requested 3 galaxies, of which 85% will be spent observing central positions and 15% in offset observations. We think this time request is reasonable if spread over a multi-semester campaign running over a period of around 3 years, i.e. an average allocation of 1 hours per semester.

3 A Legacy Survey to Study Cold Gas Scaling Laws in the Local Universe Perhaps the most fascinating aspect of nearby galaxies is the intricately interwoven system of correlations between their global properties. These correlations form the basis of the so-called scaling laws, which are fundamental because they provide a quantitative means of characterizing the physical properties of galaxies and their systematics. Galaxy scaling laws also provide the route to understanding the internal physics of galaxies, as well as their formation and evolutionary histories. We currently enjoy a rich and diverse array of scaling laws that describe the stellar components of galaxies. The Tully-Fisher relation and the size-mass relation for local spiral galaxies play a crucial role in constraining current theories of disk galaxy formation. These theories hold that disks form when gas cools and collapses within dark matter haloes until it reaches centrifugal equilibrium. The observed size-mass relation is consistent with the idea that the angular momentum of the infalling gas originated from tidal torques during the initial collapse of density perturbations in the early universe, and that this angular momentum was largely conserved during the subsequent collapse of the gas to form the disk. It is also consistent with the idea that disk galaxy formation continues right up to the present day (e.g. Fall & Efstathiou 198; Kauffmann 1996; Mo,Mao & White 1998) Likewise, the scaling laws of bulge-dominated galaxies (the Fundamental Plane) provide important constraints on how these systems have assembled through merging. The stellar mass-metallicity relation is fundamental to our understanding of the fraction of metals injected into the intergalactic medium by supernovae-driven winds. The discovery of a close correlation between black hole mass and bulge mass led to the idea that black holes may play an important role in regulating the growth of galaxies. Galaxy scaling laws should not just be regarded as important in our understanding of nearby galaxies. Now that high redshift astronomers are switching from discovery mode to more systematic studies of larger samples, attention is focusing on understanding if and how the scaling relations defined at low redshift have evolved with cosmic epoch. It is remarkable, therefore, that so few well-established scaling laws exist describing how the cold gas is correlated with the other global physical properties of galaxies. The only well-studied scaling law is the relationship between the formation rate of new stars and the surface density of cold gas in disks, the so-called Schmidt-Kennicutt star formation law. The star formation law, however, should be regarded as a local scaling relation, not a global one. It serves to constrain the local physics of the interstellar medium, rather than the global galaxy assembly processes described above. There has been surprisingly little work to understand how the cold gas is related to global galaxy properties, such as their masses, sizes and bulgeto-disk ratios. This constitutes a serious deficiency in our knowledge, because the gas is the reservoir of material out of which stars form. As such, the gas ought to be much more sensitively linked to formation processes (e.g. accretion) that are occurring now, rather than integrated over timescales of many gigayears, as is the case for the stars. We now argue that the reason why so few scaling laws involving cold gas exist in the literature and the reason why cold gas properties are not yet established as a fundamental constraint on galaxy formation theory, is simply the lack of suitable data. What data are needed to define global scaling laws between gas and stars : The major requirements for defining scaling relations are the following: 1) Homogeneous data and accurate measurements of all the physical properties under consideration. 2) Each property must be measured in an unbiased way with respect to every other property, otherwise the derived relations between the properties will themselves be biased. 3) The measurements must span sufficient dynamic range so that one can properly categorize the full scale of possible variation in each physical quantity. 4) The sample must be large enough to define the correlations, both in terms of the mean and the scatter about the mean. Nowadays, all 4 conditions listed above are routinely met by optically-selected samples of galaxies at low redshift. In particular the Sloan Digital Sky Survey (SDSS) has obtained 5-band optical imaging data over a quarter of the sky, and high S/N spectra covering the wavelength range from 38 to 92 Å with a resolution of 2 for a sample of 7, galaxies. The SDSS will stand as the main Legacy Survey of nearby galaxies at optical wavelengths for decades to come. The study of atomic gas in nearby galaxies will benefit from a new generation of blind HI surveys covering wide areas of the sky. The most advanced among these is the Arecibo Legacy Fast ALFA Survey (ALFALFA; Giovanelli et al 25), which will detect more than 2, extragalactic HI line sources out to z.6. Although ALFALFA survey data are accurate, homogeneous, and unbiased with respect to any other galaxy property, the survey is shallow, with the the result that it does not probe a large dynamic range in HI-to-stellar mass ratio for all but the very nearest galaxies. Unfortunately, the situation with molecular gas observations of nearby galaxies is far worse. Homogeneous and relatively deep data does exist in the form of molecular gas maps covering the optical disks

4 of 4-6 nearby galaxies (e.g.the HERACLES survey, Leroy et al 29; Kuno et al 27). These samples are excellent for studying star formation laws within galaxies, but the number of galaxies is too small to adequately define global scaling relations. Older data are beset with a variety of uncertainties and biases: 1) Single dish observations often did not cover the entire disk of the galaxy and thus the total molecular gas content of the galaxy cannot be measured accurately. 2) The data are heterogeneous. The galaxies were selected for a variety of different reasons, often using IR luminosity as a criterion. Any scaling relation is thus likely to be severely biased. 3) Most existing catalogues only record detections and do not provide upper limits. As a result, it is impossible to assess the true dynamic range in quantities such as M(H 2 )/M or M(H 2 )/M(HI). In recent work, Cheng Li assembled CO data from the literature for 374 nearby galaxies in the SDSS survey. The vast majority of these galaxies have redshifts less than.2. The measurements were then placed on a common scale, using a common conversion factor and cosmology. More details are given in gamk/gasproblems.pdf. The resulting scaling relations are plotted in the top panels of Fig. 4. The scatter is huge and Cheng s analysis concludes that aperture problems are likely one of the major underlying causes. In addition, different telescope calibrations, low S/N detections, selection on IR luminosity, and variations in the CO-H 2 conversion factor (e.g. ULIRGs have a conversion factor 5 times lower than the Galactic one that we assumed (Downes & Solomon 1998)) all artificially increase the scatter. One contribution to solving the problem: We are carrying out the GALEX Arecibo SDSS Survey (GASS), an ongoing large targeted survey at Arecibo, home to the world s largest single-dish radio telescope. GASS is designed to measure the neutral hydrogen content of a representative sample of 1 galaxies uniformly selected from the SDSS spectroscopic and GALEX imaging surveys, with masses in the range M and redshifts in the range.25 < z <.5. Integration times are set so that we should detect all galaxies with HI mass fractions of 1.5% or more. GASS will produce the first complete sample of galaxies with homogeneously measured stellar masses, structural properties, star formation rates and atomic gas fractions measured down to sufficiently low levels to properly constrain the HI as a reservoir for future growth of galaxies in the local Universe. Observations started in March 28, and are expected to be completed over a period of 3 years. More information is available at The first GASS data release (GASS DR1) consisting of 21 galaxies will take place once our first papers (which are currently close to completion) are accepted. In Figure 1, we plot relations between the average HI-to-stellar mass ratio as a function of stellar mass and as a function of stellar surface density. The stellar surface density is proportional to M /Reff 2 ; we are thus probing the size dependence of the HI gas fraction at a given stellar mass. Interestingly, there is a strong dependence of HI fraction on surface density above M kpc, a value that was identified in Kauffmann et al (23) as marking a definitive break in the scaling relation between surface density and stellar mass. This Proposal: One intriguing hypothesis to explain why smaller, denser galaxies have lower HI fractions, is that a larger fraction of the cold gas reservoir is in the form of molecular gas (e.g. Krumholz, McKee & Tumlinson 29a,b; Obreschkow & Rawlings 29). If true, this has important implications for understanding the nature of the cold gas in L galaxies at higher redshifts, which are predicted by theory and also observed to have higher surface densitites that their local counterparts. Our new theoretical models (Jian Fu et al, in preparation) also demonstrate that the exact position of a galaxy on the cold gas scaling relations is a sensitive diagnostic of both its angular momentum and of the fraction of gas that has recently accreted from its surroundings. It is well known that cold gas consumption times in local spirals are short compared to the age of the Universe galaxies are predicted to transition through the relations following each new accretion episode. Depending on the angular momentum of the infalling gas, an accreting galaxy can start out as either HI-rich or H 2 -rich, and then migrate down to the gas-poor part of the diagram (Fig. 4). Cold gas scaling relations should thus be regarded as dynamic rather than static and they provide important insight into galaxy growth at the present day. We believe that our understanding of cold gas scaling laws will not be complete with HI surveys alone. We also need to understand if and how the balance between atomic and molecular gas changes across the local galaxy population. We are thus proposing to follow up a minimum of 3 galaxies targeted by the GASS survey with the IRAM 3m telescope. Our proposed survey will provide a definitive census of the partition of condensed baryons into stars, atomic and molecular gas in.1 1L galaxies in the local Universe. It will also meet the 4 major criteria necessary to define robust scaling laws between these quantities: 1) Galaxies in the redshift range.25 < z <.5 (i.e. 1 to 2 Mpc) have angular diameters that are small enough to enable accurate recovery of the total CO line flux with a single IRAM 3m pointing for the majority (8%) of galaxies. For the remaining 2%, simulations demonstrate that we will be able

5 to measure the total molecular mass by adding a single offset pointing and assuming azimuthal symmetry. By targeting galaxies with stellar masses greater than 1 1 M, we will be concentrating on the population of galaxies where the CO line flux is most likely to provide a reasonably accurate measurement of the total molecular gas content using a single conversion factor. Of course we will need to look for any indications that this assumption breaks down for subsets of the galaxies in our sample. Information on metallicity and dust content of the galaxy are provided by the SDSS spectra, and this should help. 2) Our sample will be selected randomly from the GASS sample, and will thus be unbiased. 3) We will integrate until the CO line is detected, or until we reach an upper limit in molecular gas mass to stellar mass ratio of.3 (i.e. similar to that achieved by the GASS survey for the atomic gas.) 4) A survey of about 3 galaxies has been demonstrated to be sufficient to determine accurately a scaling relation involving three variables, as well as to measure the scatter around the relation ( see for example the Jorgensen et al Fundamental Plane survey of elliptical galaxies in clusters). Results from our pilot observations: In the last proposal round, we were granted 8 hours of observing time (project 123-9) to carry out a pilot study of molecular gas in 15 galaxies with stellar masses greater than 1 1 M, atomic gas fractions greater than 1%, redshifts in the range.25 < z <.5, optical data from SDSS and HI data from Arecibo. The pilot program galaxies span a wide range in colour from NUV-r values characteristic of galaxies with passively evolving stellar populations, to very blue galaxies with clear ongoing star formation. The observations were carried out in June and August 29 under poor but stable weather conditions of about 1 mm of pwv. Even so, we detected 7% of the galaxies and imposed strong constraints to the molecular gas mass fraction for the non detections (M(H 2 )/M.3) (see fig. 3). We also spent a significant amount of the time observing offset positions to characterize the extent of their molecular gas distributions and to find the most efficient way to correct for aperture effects (fig. 5). Observing strategy: We base our observing strategy on the knowledge acquired from the pilot program. This strategy is designed to reduce telescope overheads as much as possible: * Thanks to the large frequency bandwidth of the new generation receivers ( 4 GHz = 11 km s at the average redshift of the GASS sample) we can observe the redshifted CO(1-) line in all our sample galaxies with a single tuning of the receivers. We will save 2 3 min per source this way. This single tuning strategy will also be extremely useful to characterize any possible calibration variations between different atmospheric conditions/observing runs, because we always look at the same lines of the selected line calibrators. The single tuning frequency covers the range from from 19.1 to GHz, so we profit from a considerably improved atmospheric transmission as compared to the CO rest frequency. Finally, we note also that the 13 CO(1 ) rest frequency lies in the observed frequency band and we can thus do line calibration using carbon stars or other nearby strong sources. * GASS galaxies are concentrated in a strip with R.A. = 1 16 hr and Dec. = 15 d (see fig. 2). That means that if a galaxy is detected quickly, it will be possible to start to observe a nearby galaxy using the pointing corrections from the previous one. * We will accommodate to the changing weather conditions by observing blue galaxies (which are expected to be bright in CO) under poor weather conditions (i.e., high pwv), and red galaxies and offset positions when the weather is good. * Because there is a large sample of galaxies to choose from, we will always be able to observe at high elevations of about 45 deg on average (i.e., low atmospheric opacities). * A central pointing will be sufficient to provide an accurate total molecular gas mass in most cases (8%, fig. 5a). We have used a compilation of 46 nearby galaxies with high-quality CO(1-) maps as a set of templates for estimating aperture effects. We place these galaxies at the redshift of the galaxies in the GASS DR1 sample and compute the fraction of the total line flux that would be recovered within the 22 beam of the 3m telescope (see fig. 5). This gives a criterion on the angular size of the galaxy, above which an offset observation is required to accurately recover the total flux. Galaxies with optical sizes larger than 4 with strong central CO(1-) lines will require an additional offset observation (at a distance.75 Beam 16 from the center, fig. 5b). Large galaxies where the CO(1-) line is weak are mainly early-type galaxies with red colours. Our pilot program demonstrated that such galaxies are never detected in the offset position, even when they have high atomic gas fractions. We will not observe offsets for these objects. Observing time estimates: (please see the technical summary on page 2 for detailed justification) We require a total of 55 hr for the requested 3 galaxies, of which 85% will be spent observing central positions and 15% in offset observations. We think this time request is reasonable if spread over a multisemester campaign running over a period of around 3 years, i.e. an average allocation of 1 hours per semester.

6 Additional Science: There are many scientific applications of a large CO survey. Here we provide a brief summary of just a few of the possibilities: An accurate CO luminosity function for massive galaxies. Existing CO luminosity functions have been derived using incomplete and inhomogeneous data sets (Keres et al 23; Obreschkow & Rawlings 29). The selection function of our survey is extremely well determined; this will enable a definitive CO luminosity function to be constructed for galaxies with M > 1 1 M. The CO linewidth as an estimator of dynamical mass. It has been claimed that HI and CO linewidths track each other very closely, but this has not been tested using galaxy samples that span a wide range in physical properties. We can also study the relationship between the total baryonic mass of galaxies (stars+cold gas) and their dynamical masses. Relations between star formation, atomic and molecular gas on galactic scales. Scaling relations between star formation and gas surface density have been studied in detail for small samples of nearby spirals. How well do the results extrapolate across the whole galaxy population? Ancillary UV data from GALEX and IR data from Spitzer/Herschel can be combined with our HI and CO data to answer this question. We can also search for any molecular mass that is undetected in CO (e.g. because it is photo-dissociated) by comparing with the molecular mass inferred from the IR. Do AGN influence the cold gas in nearby galaxies? The SDSS spectra provide very useful information about the AGN content of the galaxies in our sample around 3% of the galaxies in our sample have a central LINER or Seyfert nucleus. Morphology of the gas. In galaxies where he have offset observations, we will have an estimate of the concentration of the gas. The expected (local) pointing accuracy is about 1, allowing us to study asymmetries in the line profiles and ask whether they are correlated with other properties of the galaxies, such as their star formation rates. Molecular gas in elliptical galaxies. Even if we do not detect the CO line for individual objects, the spectra can be stacked and one can still derive average molecular gas fractions for classes of galaxies that are gas-poor, such as ellipticals. Program Management: Our team of multi-wavelength observers and theorists encompass a wide range of expertise and talents that will allow us to make sure that this data set is of lasting legacy value for the full astronomical community. ** G. Kauffmann and C. Kramer will be responsible for the overall program management and coordination. They will maintain communication to IRAM, as well as teams from the two other facilities (ARECIBO and GALEX) that are involved with the GASS program. Communication will be enhanced by regular team meetings. A dedicated project wiki portal will be created, to inform the public, and to allow all Co-I s to coordinate their work in an efficient way (see, for example, the GASS portal ** A. Saintonge, J. Gracia-Carpio and L. Tacconi will be in charge of the observations, data reduction and analysis. They will be aided by a team of observers (Buchbender, Catinella, Fabello, Li, Rodriguez- Fernandez, Sievers). We hope to carry out a substantial fraction of the observing remotely from Garching or from IRAM, Granada. The involvement of experts from IRAM will ensure a uniform and homogeneous data product. ** We suggest that this project be scheduled during the pooled weeks, as a poor weather backup project. Our pilot study clearly showed that we can detect significant fraction of the galaxies, even when the amount of pwv is high. One of the advantages of using the pool and its database is that logs are automatically created and the project progress can easily be followed. We will also staff the pools. ** We have substantial experience and expertise in the acquisition, processing and analysis of ancillary data. B.Catinella and D.Schminovich lead the processing of the HI observations of the GASS sample, and work closely with R.Giovanelli and M. Haynes on the interface between GASS and ALFALFA. J. Wang is expert on photometric processing of GALEX and SDSS data. S. Moran leads an effort to obtain follow-up long-slit spectroscopy for the GASS sample. L. Cortese is planning to work on Herschel observations that will cover many galaxies in the GASS sample. ** Our team includes theoreticians (PhD student Jian Fu, Qi Guo, Kauffmann, Krumholz) who are building new galaxy formation models that track the evolution of both atomic and molecular gas in the Millennium Simulation (see Fig. 4). ** We expect that the initial scientific analysis and exploitation of the data be led by the postdocs and students working in consultation with the more senior members of the team. ** After acceptance of the first set of papers, our intention is to release the data in user-friendly, VOcompatible form to the entire astronomical community in a series of yearly data releases.

7 Figure 1: Recent results from the GASS HI survey. We plot the average value of the HI-to-stellar mass ratio as a function of stellar mass (left) and stellar surface density (right). The difference between the red and the green symbols indicate the remaining uncertainty the mean scaling relation due to HI non-detections. The blue points are galaxies detected by the ALFALFA survey in the same redshift range. Clearly the ALFALFA galaxies are biased towards very HI-rich systems. Figure 2: Distribution on the sky (in horizontal coordinates) of our sample galaxies during a typical observation with the 3m telescope. The zenith is situated in the center of the figure. References Downes,D & Solomon, P.M., 1998, ApJ, 57, 615 Giovanelli, R. et al., 25, AJ, 13, 2598; Helfer, T.T., et al. 23, ApJS, 145, 259; Joergensen, I., Franx, M., Kjaergaard, P., 1996, MNRAS, 28, 167; Kauffmann, G., 1996, MNRAS, 281, 487; Kauffmann, G. et al., 23, MNRAS, 341, 54 Krumholz,M.R., McKee,C.F., Tumlinson,J.,29a,ApJ, 693,216; Krumholz,M.R., McKee,C.F., Tumlinson,J.,29a,ApJ, 699,865; Kuno, N. et al., 27, PASJ, 59, 117; Leroy, A. et al 29, AJ, 137, 467; Mo, H.J., Mao, S., White, S.D.M., 1998, MNRAS, 295, 319; Obreschkow,D., Rawlings, S., 29, ApJ, 696, L G G G G G G G Figure 3: Recent results from our pilot program. We show examples of CO line detections (first 5 galaxies), and 2 galaxies where M(H 2 ) was constrained to be less than.3 M.

8 log 1[MH2/M ] log 1[MH2/M ] lg[m /M ] lg[m /M ] log1[mh2 /M HI] log1[mh2 /M HI] Old Data log 1[MHI/M ] lg[µ /M kpc ] lg[µ /M kpc ] Model results THINGS PILOT.5.5 log 1[MHI/M ] lg[µ /M kpc ] lg[µ /M kpc ] Figure 4: Scaling relations between molecular gas fraction and stellar mass (left), molecular-to-atomic gas ratio and stellar surface density (center), and atomic gas fraction and stellar surface density (right). The top panels show results for a compilation of nearby galaxies from SDSS with HI data from the HyperLeda catalogue and CO data from the literature. We have done our best to ensure that the CO measurements have been put on a common system with regard to conversion factor etc. In the bottom panel, we show the same scaling relations for galaxies drawn from the THINGS/HERACLES survey (red) and from our pilot program (blue circles denote detections, and blue triangles denote upper limits). The grey points are from new galaxy formation models that include both the molecular and atomic gas phases (Jian Fu et al, in preparation). In the top panels, the scatter in quantities involving the molecular gas is huge. It is larger than predicted by the models and is inconsistent with our newer data. In contrast, the atomic gas scaling relations look quite comparable to both the models and our more recent data. The limit in M(H 2 )/M that we plan to reach with the proposed survey is plotted as a dashed line in the figure. As can be seen, the majority of the model galaxies lie above the line. The model galaxies scattering below the line are gas-deficient for two main reasons: a) some are satellite galaxies in groups and clusters that have consumed most of their gas, b) others are galaxies with small spin parameter that have not experienced a recent episode of gas accretion. I CO(1 ) (center) / I CO(1 ) (total) a) I CO(1 ) (center) / I CO(1 ) (total) b) I CO(1 ) (offset) / I CO(1 ) (center) c) D 25 [ arcsec ] I CO(1 ) (offset) / I CO(1 ) (center) D 25 [ arcsec ] Figure 5: 3m telescope aperture correction study for galaxies situated at the GASS redshift range (.25 < z <.5). a) Relation between the optical diameter of the galaxy (D 25 ) and the fraction of CO(1-) line flux recovered at the center with the 22 beam of the 3m telescope. Small points indicate the results from the simulated observations of a sample of 46 nearby spiral galaxies with high-quality CO(1 ) maps (Kuno et al. 27; Helfer et al. 23) when they are placed at z=.5 (red points), z=.35 (green points), z=.25 (blue points) and z=.15 (grey points). A single central observation recovers most (> 7 %) of the CO line flux in galaxies with D 25 < 4. The histogram indicates the optical size distribution of the GASS sample (the distribution of red galaxies is indicated in red). As can be seen, most of the largest galaxies are red and we do not expect to observe offsets for these. b) With an additional offset observation it is possible to derive the fraction of CO(1-) line flux detected at the center and from that estimate the total molecular gas mass in galaxies with D 25 > 4. The offset is situated at a distance of.75 Beam ( 16 ) from the center of the galaxy in the direction of the optical major axis. We tested different values of the separation and found.75 times the Beam to provide a reasonable compromise in terms of our ability to probe the structure of the molecular gas, while still retaining enough intensity in the CO line in the offset position. Big black points in a) indicate the aperture corrections estimated for some of the sources of the pilot survey using this technique. c) CO lines are typically.3.4 times weaker in the offset position than in the center position for galaxies with D 25 > 4.

9 This source list comprises the 21 galaxies currently observed in HI by the GASS survey (GASS DR1). We will start our CO observations from this sample and incorporate new galaxies as soon as they are observed in HI with Arecibo. Extended source list (cont d from cover page) Source RA Dec LSR Velocity (J2.) (J2.) (km/s) G :33: :57: G :47: :26: G11 14:52: :8: G119 14:51: :21: G :58: :6: G :11: :4: G :6: :58: G :13: :3: G :26: :1: G11956 :8: :9: G11989 :25: :55: G :13: :14: G :4: :21: G :5: :4: G :4: :1: G1764 1:59: :42: G :18: :: G :32: :44: G :34: :: G2144 9:35:2.2 +9:55: G2286 9:54: :26: G :23: :51: G :56: :52: G :17: :25: G :2: :42: G :51: :46: G :4: :4: G :37: :39: G :58: :25: G :21: :25: G :23: :18: G341 12:34: :33: G :57: :15: G :5: :59: G :5:8.3 +9:4: G :5: :12: G :47: :13: G :47: :25: G :47: :32: G :27: :37: G :27: :2: G424 13:33: :14: G :47: :17: G :57:4.5 +1:37: G :19: :27: G :15: :22: G :16: :14: G :12: :13: G :15: :1: G :16: :9: Extended source list (cont d from cover page)

10 Source RA Dec LSR Velocity (J2.) (J2.) (km/s) G :15: :28:4.5 z=.498 G :22: :31: G :35: :41: G964 14:3: :16: G :28: :15: G :34: :2: G :33: :57: G5717 9:22: :27:43.4 z=.3232 G759 14:3: :5: G :59:5.4 +5:2: G :2: :4: G :17: :43: G :57: :24: G :15: :26: G :48: :3: G :2: :55: G :42: :46: G :25:5.5 +3:13: G :58: :17: G :36: :18: G :2: :51: G47 13:35: :19: G :49: :45: G :5: :11: G75 13:49: :45: G :14: :11: G :27: :5: G :39: :43: G957 14:2: :6: G974 14:4: :8: G :39: :22: G :42: :13: G :4: :35: G131 14:51: :5: G14 14:52: :32: G115 15:: :1: G :13: :7: G :17: :21: G :15: :3: G144 15:17: :12: G :18: :25: G :1: :11: G :14: :4: G1225 :19: :12: G :2: :19: G :21: :39: G :2: :5: G :36: :1: G :43: :5: G :4:47. +3:54: G :45: :48: G :16:.2 +6:15: G :58:7.6 +9:16: Extended source list (cont d from cover page)

11 Source RA Dec LSR Velocity (J2.) (J2.) (km/s) G299 14:38: :2: G :48: :29: G :8: :13:27.6 z=.341 G :37: :16: G :37: :24: G358 12:59: :2: G :18: :5: G :16: :35: G :9: :35: G :17: :34: G :2: :3: G :2: :17: G :19: :5: G :19: :8: G :25: :47: G :27: :46: G :59: :44: G :58: :27: G :55: :45: G45 12:59: :3: G457 13:11: :48: G :15: :51: G479 13:19: :21: G :18: :5: G :31: :19: G :17: :44: G :15: :26: G422 15:15: :39: G :15: :28: G :17: :29: G :18: :7: G912 11:1: :2: G8695 1:23: :8: G :48: :2: G :55: :59: G :53: :14: G :33: :52: G :18: :6: G :27: :46: G :1: :25: G :7: :53: G :47: :39: G :34: :14: G8748 1:33: :15: G :55: :2: G :2: :53: G2674 8:28: :38: G478 13:33: :12: G8724 1:22: :34: G :3: :51: G :26: :23: G :59: :47: G :49: :3: G :13: :51: G :5: :5: G :46: :1: G :47: :55: Extended source list (cont d from cover page)

12 Source RA Dec LSR Velocity (J2.) (J2.) (km/s) G :11: :7: G :25: :49: G :33: :12: G :18: :34: G :51: :45: G :49: :56: G :59: :13: G :21: :5: G189 1:2: :3: G :56: :29: G2348 1:53: :1: G2345 1:56: :5: G :2: :2: G :4: :4: G :12: :43: G :3: :3: G :6: :3: G2662 1:33: :43: G :46: :53: