Terapix Star Formation Region IC 1396, © 2002 CFHT
Minutes for VIRMOS science meeting Marseille 28th-29th April 2005
by HJMCC - Updated February 24th, 2006

Minutes for VIRMOS science meeting

Marseille April 28th-29th 2005

Schedule distributed by Olivier before the meeting

Present: Gigi Guzzo, Angela Iovino, Olga Cucciati, Paolo Franzetti, Lucia Pozetti, Marco Scodeggio, Alberto Cappi, Olivier Ilbert, Laurence Tresse, Baptiste Meneux, Alain Mazure, Vincent Le Brun, Dario Maccagni, Bianca Garilli, Christophe Adami, Agnieska Pollo, Olivier Le Fevre, Fabrice Lamareille (from the afternoon of the second day onwards), Stephane Palatani

Action items:

-  Olivier calls for ideas for a next set of proposals
-  Olivier suggests that interesting figures are uploaded to the paper repository which are then put on the VIRMOS web pages by Laurence

(Note: Olivier has lost his laptop, and missed the start of the meeting. The sessions were rearranged accordingly, with the afternoon sessions for the afternoon of the first day moved to the morning.)

Lucia Pozzetti presentation: stellar mass function


There are three methods to compute the stellar mass function which are:

-  Photometry + hyperz (work carried out by Lucia and Micol )
-  Photometry + binned spectroscopy (by Franzetti & Scodeggio)
-  Spectral features (D4000,Hdelta) (by Lamareille,Meneux,Charlot)

-  We use modified version of hyperz trained by spectroscopic redshifts and using photometric data (using data from U to K)

-  Simulations (no cfhtls data used in this test) show an accuracy of around 1.6 using UBVRIJK up to z 3 and around 2 using only UBVRI at z<1 and 4 and z>1.

-  The results for the K-selected sample (694 galaxies) show that there are massive galaxies at z around 1. Note that this data is limited at IAB<24.0; at K<22 we are not complete because our data is constructed from an I-selected sample.

-  If we use only UBVRI data optical data we overestimate masses at high z.

-  Comparison also shown between Paolo Franzetti's spectrophotometric mass estimate and photometric mass (MB & LP) estimates: agreement is pretty good.

-  Now try with K-selected sample (selected simply in K); there is good agreement between purely photometric and spectroscopic sample except at z>1.5, because the numbers of galaxies is too low

-  There is a good agreement with K20 survey but it extends around one magnitude fainter, i.e., lower mass limit. Lower mass galaxies evolve more rapidly than higher mass galaxies. In the hierarchical models have a deficit of high-mass galaxies.

-  Finally, the IAB<24 selected spectroscopic sample; IAB<24, n 6400 galaxies. Good agreement in the MF up to z 1; overestimate mass function higher redshifts. Conclusions: I-band sample is best at low redshifts (z<1)

-  SWIRE photometry has been added added to optical data improve mass estimate (uncertainties less than 1.5 up to z 3 from simulations). MF derived for IAB<24 selected spectroscopic sample using optical+swire photometry (6400 gal.). MF swire selected could be derived using photometric redshifts to have a "mass"-selected sample.

Baptiste Meneux (presentation): clustering of galaxies of type 1, 2, 3 and 4. baptiste.meneux@oamp.fr

-  Type defined by spectra fitting using tool from Olivier Ilbert. For all types we derive a clustering length r0 which is constant with redshift.

-  These results are difficult to interpret because at each slice in redshift we have increasingly brighter galaxies and it can be difficult to disentagle morphological clustering effects and luminosity effects.

-  Error bars are computed with bootstrap method: unfortunately, gallics simulations are not robust enough

Christophe Adami presentation: Using friends of friends algorithm to locate structure in the 02hr field using spectroscopic and photometric redshifts.


-  Using this method in the the CDFS field we found two walls at z 0.66 and z 0.73; also a large wall at z 1.0.
-  In the F02 field the sampling rate is slightly better than than CDFS field. With spectroscopic redshifts, we find 56 structures in 0.17-  These structures are mostly diffuse
-  Using photometric redshifts several significant galaxy overdensities are discovered which match those found using in spectroscopic redshifts in well-sampled regions.
-  For example, a large structure is found at z 0.64 in the spectro data. Five close independent structures also found.
-  Systematic comparisons are necessary between zphot and zspec finding algorithm are necessary. In zphot we find "rich" structures and with with zspec we find "compact" structures.

Angela Iovino presentation: Discovery of a z 1.47 cluster using Christian Marinoni's cluster finding algorithm.


-  This structure is a 5-10 sigma overdensity. Size of the structure is around 10 Mpc.
-  Nine of these 16 galaxies are found within a single FORS2 field (7x18 field); this should be be compared with mulis et al.
-  A second search was made with photometric redshifts and for objects which have 1.3-  Structures found with zphot are consistent with the presence of a "cluster". The I-CFH12K data is not deep enough to find these structures alone.
-  The i* legacy survey data should be deep enough.
-  Plot made with i-j, j-k using legacy survey data seems to back up the existence of a cluster; the candidates are in correct locus in the colour-colour plot.

Olga Cucciati presentation: Estimating density fluctuations in F02. cucciati@brera.mi.astro.it

-  Would like to be able to study evolutionary effects as a function of environment
-  Many simulations carried out to find optimal filter for extracting density field (combinations of r and z)
-  Apply corrections for sampling rate, incompleteness and boundary effects
-  Some results shown for the VVDS with r=4.0
-  Unbiased reconstruction is only possible for r>4.0

Fabrice Lamareille presentation: Estimating masses from spectrophotometric data flamare@ast.obs-mip.fr

-  Unlike at the last meeting the work has been presented with actual data and NOT simulations.
-  Using Bruzual and Charlot models we try to derive the mass-to-light ratios.
-  We can't use the standard Lick indicies because the VVDS resolution is not good enough; instead we define new indicies
-  Output distribution matches input distribution from the models (simulations).
-  Finally, plots were shown comparing "spectroscopic" masses and "photometric" masses.
-  Estimates are simliar but the spectroscopic estimates are less sensitive to dust.
-  Seems no dependence on redshift; it is also found that the specific star-formation rate decreases with mass; more massive galaxies are undergoing more star-formation in VVDS data
-  With around 50 galaxies however, the statistics are small; need to add more galaxies).

Vincent Lebrun presentation: Status of wide survey data processing. vincent.lebrun@oamp.fr

-  Summary of supercheck sessions:6 supercheck sessions so far, average of 7 fields per time.
-  Still half of the F02 field still to be processed
-  Olivier suggests next super-check session at 19-23 September 2005

(coffee break)

Olivier, Bianca: public availability of vipgi and other tools
-  Bianca mentions that currently one person arrives each month at Milan to reduce data which is a non-negligible load on resources; by making VIPGI public this would reduce this responsibility
-  If VIPGI is released, the release will be a binary release (no sources).
-  Development of next-generation tools
-  KBRED and YAZ: YAZ is a simplified version of VIPGI; the source for this tool has been made available to the consortium.
-  Stephane Palatani volunteers to work on YAZ and producing a C/python version, in possible collaboration with Paolo Franzetti who will help with the VIPGI interface

Further discussions on the mass function (OLF)
-  It seems that by adding the SWIRE data to the VVDS dataset, the improvement on the mass function accuracy is minimal
-  We should just use the VVDS data rather than adding all the SWIRE team, given the improvments are minimal.
-  Luminosity density measurements: Laurence and Olivier mention that there is a problem with incompleteness correction.
-  Olvier Ilbert and Stephane Arnouts will look at the possibility of using a random catalogue to estimate the incompleteness

Second day Dario Maccagni: XMDS sources (presentation) dario@mi.iasf.cnr.it

-  Probably some missing low surface brighness extended sources
-  286 X-ray sources in F02 field (s/n of 4 in at least one band)
-  29 of these sources have redshifts
-  14 broad line QSOs (
-  3 stars, 12 galaxies (6 safe and unique identfications)
-  For the moment, statistics are too small, need more spectra or redshifts
-  The important question to answer is: what the relationship between the X-ray galaxies and the general population?

Gigi Guzzo presentation: Bimodal colour distributions guzzo@merate.mi.astro.it
-  Review of bimodal colour distribution observations in the sloan/combo17 .
-  Blue and red populations have different clustering properties
-  COMBO-17 bimodality; Bell et al.
-  Evolution of the red and blue luminosity function with redshift
-  Other paper looks at HST imaging of these galaxies
-  Many interesting topics to be addressed.

Paolo Franzetti presentation: Bimodal colour distributions


-  Several approaches used to compute the absolute magnitude
-  Bimodal colour distributions visible at IAB 23 but not at fainter magnitudes
-  Grid of bins in redshift and luminosity shown
-  Bimodality observed in several colour combinations
-  It's quite important to make sure the evolution observed is not due to selection effects.
-  Some work has been done with "best available" zphot to see how the sample can be englarged; seems that the errors in recovered colours is small enough to make this an interesting proposition

Agnieszka Pollo: presentation Correlation function measurements with luminosity cut apollo@merate.mi.astro.it

-  Two bins in z, 0.3 and 0.8 are defined, local and distant.
-  We see a clear dependence in both bins on luminosity
-  For the galaxies at z 0.8 the luminosities are distributed in redshift
-  Some attempt has been made to construct a volume limited sample

(Coffee break)

OLF: LRBLUE (25-30 objects) observed in directors discretionary time. Processing still has to be done.

OLF presentation: List of papers and work in progress Olivier.LeFevre@oamp.fr

-  Discussion of papers submitted, accepted or in press with the various authors
-  Discussion of papers in preparation
-  OLF suggests providing a functional fit to the dndz distribution which could be used for those producing simulations
-  Bianca will help Angela to examine the templates for the J-K paper
-  OLF raises the possibilty of constructing a J-selected sample. Angela will investigate.
-  OLF insists that the GALEX fluxes for virmos objects should be made available
-  Henry will produce a combined CFHTLS+cfh12k mask for correlation function work

(Lunch) Plan for next observing proposals, organisational matters (OLF)
-  Arrange a telecon in the next month to discuss which proposals to submit after the next OPC meeting at the end of May
-  For example, extending covering to large ( 20 deg2) scales
-  Need to gather interesting plots together on a web page for use by people outside the consortium
-  Need to think about text for a possible press release for a nature paper
-  Data policy: would like to make deep epoch I: data public in January 2006. Vincent and Laurence will make recommendations on how to proceed with the next public release
-  Next science meeting 12th, 13th of July in Bologna

Special swire session (Stephane Arnouts and Michael Rowan-Robinson)

Photometric redshifts in SWIRE (Stephane Arnouts); using only the bluest passbands from IRAC combined with the photometric data.

-  Neural networks (Seb Oliver)
-  MRR photometric redshift code
-  Le Phare (Stephane Arnouts)

The photometric redshifts seem to be robust up to z<1.3.

With the three codes we can investigate in detail the properties of the outliers and the AGN contribution

-  We need to improve the star-galaxy-qso separation
-  We can derive the FIR fits using all the SWIRE bands
-  Which zphot should we add to the database?

-  SWIRE + VVDS interesting in the redshift range
-  6-7 % in (1+z)

Not presented: Roberto Scaramella presentation An analysis of the comparison of the distribution in depth (i.e. mono dimensional) of structures in CDFS as seen in the VVDS with those found in X-ray sources. Limited to z<1.2 (cf Adami at al results)

-  Derived and adaptive estimate of the 1D optical density field n(z)

-  1) Good correspondence with the three highest peaks seen in K20 (which has a much smaller area) and in X-ray

-  2) Similar distribution in z of X and optical sources (within z=1.2)

-  3) passing to overdensity, dn(z)/, do not find a segregation of X w.r.t. optical (i.e. no preference of X locations). A slight 'hint' of preference for denser regions is not significant according to a KS test (which is not very powerful).

-  4) comparing X & optical self overdensities (always 1D ones!!) find a strong relative bias (factor of 2), hence stronger clustering of X vs optical (as just found from a xi analysis of X)

Next VIRMOS science meeting:

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