IPHAS DR2

Seminar for the Isaac Newton Group of Telescopes (ING) in La Palma.

IPHAS DR2 is the Second Data Release of the INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS).

Transcript

1. The INT Photometric Hα Survey (IPHAS) Second Data Release A seminar by Geert Barentsen for the ING in La Palma on 25 October 2013
2. IPHAS is a 1800 deg2 INT/WFC survey of the entire northern Galactic plane in r, i, Hα down to ~20th magnitude. I will tell you about: 1. Survey design and aims 2. The new data release - quality control - re-calibration - catalogue building 3. Outstanding challenges and future opportunities
3. INT/IPHAS & UVEX VST/VPHAS UKIDSS/GPS VISTA/VVV SCUBA-2/JPS & SASSy Herschel/Hi-GAL Prof Janet Drew Dr Phil Lucas Dr Mark Thompson I am a postdoc in the galactic plane surveys group at the University of Hertfordshire (UK)
4. In the past six months, we have created a new public data release called “IPHAS DR2” ‣ 67 047 WFC exposures checked for quality. ‣ Photometry re-calibrated using exposure overlaps. ‣ Catalogue generated for 220 million unique sources. New website: www.iphas.org
5. 1. Survey design and aims
6. IPHAS is the first ~arcsecond-resolution digital Hα survey of the Galactic plane ‣ Footprint covers the entire northern plane, 180 by 10 deg2. ‣ Taking data since 2003, DR2 is now 93% complete. ‣ Biggest program in the history of the INT (300+ nights)
7. r’ i’ Hα IPHAS collects r, i, Hα photometry down to ~20th magnitude ‣ About 1000 times (7 magnitudes) deeper than previous northern plate surveys. ‣ Exposure times are 120 s (Hα), 30 s (r), 10 s (i). ‣ r, i, Hα images taken ~simultaneously at each pointing.
8. Data is taken in “fieldpairs” to account for gaps and defects in the WFC ‣ Each pointing is paired with an offset at 5 arcmin S/W. ‣ “Simultaneous” observing sequence: Hα, r, i, <slew>, Hα, r, i. ‣ Low overheads because filter changes and slews are performed during readout (until recently).
9. Area coverage is efficient, only 0.3% is lost in gaps
10. The survey area requires 7635 fieldpairs = 45810 single-band exposures
11. So why are we doing this?
12. Hα in emission is a tracer for diffuse ionised nebulae ‣ new star-forming regions ‣ new planetary nebulae ‣ new supernova remnants IPHAS survey area Image: Nick Risinger
13. Discovery of the "Príncipes de Asturias" nebula (Mampaso et al. 2006) Image: Mampaso, Corradi / IPHAS
14. Discovery of the Ear Nebula (Sabin et al. 2009) Image: Sabin, Wright / IPHAS
15. Discovery of the Necklace Nebula (Corradi et al. 2011) Image: Wright / IPHAS
16. Discovery of new supernova remnants (Sabin et al. 2013)
17. Discovery of photo-evaporating objects in the Cygnus OB2 star-forming region (Wright et al. 2012) Image: Wright / IPHAS
18. Dust lanes and globules in the Rosette star-forming region Image: Wright / IPHAS
19. AV = 5 IPHAS also reveals spatially unresolved point sources with Hα in emission
20. Hence IPHAS enables the discovery of large samples of stars in the crucial stages of stellar evolution ‣ Pre-main sequence stars e.g. T Tauri,Herbig Ae/Be objects ‣ Post-main sequence stars e.g. some AGBs, compact PNs, LBVs, classical Be’s ‣ Interacting binaries e.g. symbiotic stars, cataclysmic variables (Corradi et al. 2008)
21. Discovery of 124 new pre-main sequence stars in IC 1396 (Barentsen et al. 2011) Image: Barentsen / IPHAS
22. Discovery of 124 new pre-main sequence stars in IC 1396 (Barentsen et al. 2011) Image: Barentsen / IPHAS Figure 4. IPHAS colours of known T Tauri stars in IC 1396 from Sicilia-Aguilar et al. (2005). Green squares are classical T Tauri stars (CTTS) with spectroscopic EWH↵ stronger than - 10 ˚ A. Red triangles are weak-line T Tauri stars (WTTS) with EWH↵ weaker than -10 ˚ A. The solid line shows the simulated main sequence curve at the mean reddening of the cluster ( ¯ AV = 1.56). Dashed lines shows the position of stars at increasing levels of H↵ emission as predicted by our simulated tracks. Grey dots show field stars in the region. The arrow shows the reddening shift for an M0V-type object being reddened from AV = 0 to AV = 1.56 (note that the true reddening tracks are curved in a way that depends on the SED and the amount of reddening, see Drew et al. 2005) -1 -10 -100 Spectroscopic EW [ ˚ A] -1 -10 -100 IPHAS Photometric EW [ ˚ A] Figure 5. Comparison of IPHAS photometric EWH↵ with spec- troscopic values from Sicilia-Aguilar et al. (2005). The grey dashed line shows the unity relation. The scatter is thought to be dominated by natural H↵ emission variability. well as classical T Tauri stars (CTTS) with emission stronger than -10 ˚ A EW. Out of the 118 probable T Tauri members confirmed by T Tauri candidates in IC 1396 using IPHAS 5 Figure 4. IPHAS colours of known T Tauri stars in IC 1396 from Sicilia-Aguilar et al. (2005). Green squares are classical T Tauri stars (CTTS) with spectroscopic EWH↵ stronger than - 10 ˚ A. Red triangles are weak-line T Tauri stars (WTTS) with EWH↵ weaker than -10 ˚ A. The solid line shows the simulated main sequence curve at the mean reddening of the cluster ( ¯ AV = 1.56). Dashed lines shows the position of stars at increasing levels of H↵ emission as predicted by our simulated tracks. Grey dots show field stars in the region. The arrow shows the reddening is the typical reddening found by SA05). We notice that the classical T Tauri stars are well separated from the field stars (shown as grey points): most are above the 10 ˚ A EW boundary as predicted by the drawn grid lines. In con- trast the weak-lined stars fall within the main stellar locus, blending in with normal less-reddened stars. The fact that reddening raises the EW threshold for the clean detection of emission line stars is a recognised property of the IPHAS colour-colour plane (see Drew et al. 2005). One weak-lined object, named 73-537 in SA05, can be seen to fall somewhat below the simulated main sequence (solid line in Fig. 4). The aberrant position is explained by the high reddening of the object, AV = 3.3, which is an outlier in terms of reddening compared to the rest of the sample. To validate the grid in more detail, we interpolated the tracks to derive H↵ EWs for the known T Tauri objects. These values are then plotted against the spectroscopic val- ues from SA05. The comparison is shown in Fig. 5. We find a strong correlation between the photometric and spectro- scopic estimates, albeit with a large scatter on the order of
23. 2005MNRAS.362..753D (Drew et al. 2005) Main sequence Reddening And the legacy of IPHAS is set to extend beyond ‘traditional’ Hα object identification, because the (r - Hα) colour is also a proxy for intrinsic colour.
24. (Sale 2013) IPHAS allows interstellar extinction to be mapped in three dimensions ‣ Hα, when combined with r/i/J/H/K, offers a first-order spectroscopic parallax and extinction estimate for 108 stars. ‣ Will aid the upcoming ‘Gaia revolution’. Distance Extinction
25. To exploit the survey, it is necessary to build a quality-checked and calibrated catalogue. => DR2 Source Catalogue
26. 2. The new data release - quality control - photometric re-calibration - catalogue building
27. ING Cambridge Hertfordshire Raw images Calibrated images & detection lists {Irwin, Gonzalez-Solares, Lewis, et al. (CASU) ‣ bias, non-linearity, dark, flat, fringe correction; ‣ astrometric calibration; ‣ nightly zeropoint calibration; ‣ source detection and measurement. IPHAS data flow {Barentsen, Farnhill, Drew, Greimel, et al. ‣ quality control; ‣ homogeneous re-calibration; ‣ catalogue generation (band-merging, warning flags).
28. 2. The new data release - quality control - photometric re-calibration - catalogue building
29. Median seeing at the INT is 1.2 arcsec (in our red filters)
30. Due to repeat observations, 65% of DR2 will be based on seeing better than 1.2”
31. Fortunately, we found the photometry to be acceptable up to ellipticity < 0.3 6% of our pointings suffered from ellipticity > 0.2 in at least one band
32. Poor ellipticity is most common in the longest exposure, but in 2005 it also affected short exposures. In 2005, the INT experienced a stabilisation problem
33. Limiting magnitude in the r-band
34. Limiting magnitude in the r-band
35. Limiting magnitude in the r-band
36. Limiting magnitude in the i-band
37. We systematically checked for clouds or noise by cross-matching the fieldpairs
38. Clouds, electronic noise or scattered light can be detected by checking for inconsistent fieldpair photometry
39. Clouds
42. Ha r’ i’
43. Electronic noise
49. Scattered light
50. Scattered light affects at least 800 pointings. In this image, the moon is 42° away, but it is full and at 86° altitude.
52. The effects of scattered light are clearly visible in 5°x5° mosaics
53. (1) Fieldpair consistency reject outliers at the 95%-level (2) Limiting magnitude r > 20, i > 19, Hα > 19 (3) Seeing < 2.5 arcsec (4) Ellipticity < 0.3 (5) Eye-balling. Photometric diagrams and colour mosaics. 94% of the survey footprint now passes Quality criteria
54. 2. The new data release - quality control - re-calibration - catalogue building
55. Nightly standard field observations did not provide a satisfactory calibration ‣ 9% of DR2 had to be re-calibrated by >0.1 mag. ‣ Rapid zeropoint variations are common due to high clouds, transparency changes and WFC exposure time foibles. ‣ Surveys with dedicated telescopes can discard non-photometric nights, but IPHAS time was limited. Solution: we computed the magnitude offsets across (a) exposure overlaps and (b) against the APASS survey, and then found the zeropoints which minimised these offsets.
56. Post-calibration: consistent with SDSS to within 3% (one sigma)
57. 2. The new data release - quality control - re-calibration - catalogue building
58. Catalogue building required several steps 1. Apply re-calibration. 2. Band-merge the r, i, Hα detections. 3. Create user-friendly columns and warning flags (we followed UKIDSS conventions). 4. Flag the ‘best’ detection of each unique source. The result is a huge FITS table (50 GB) ‣ 220 million unique sources with SNR > 5 in one band; ‣ 109 million with SNR > 5 in all bands.
59. Credit: Hywel Farnhill IPHAS DR2 stellar density map
60. Credit: Hywel Farnhill IPHAS DR2 stellar density map
61. IPHAS stellar densities constrain Galactic models (Farnhill et al., in preparation)
62. Catalogue is ready and is available to the collaboration for review ‣ ~1 GB FITS tables, each covering 5x5 square degrees. ‣ Talk to us if you want to join the review. ‣ Public release will be available via SQL through CDS/Vizier, once the accompanying paper is accepted (in preparation).
63. Catalogue contains all sources having SNR > 5 in at least one band
64. nBands == 3
65. nBands == 3 & r < 20
66. Bright neighbours indicated
67. Red areas demonstrate where vignetted = True criterion: (distance_optical_axis + 2*distance_ccd_centre) < 7900 px
68. Red areas demonstrate where truncated = True
69. Red areas demonstrate where badPix > 0
70. Catalogue pipeline is made available as an open source Python package ‣ Parallelised (~500 CPU hours) ‣ Depends on the “astropy” library (wraps cfitsio, libwcs) ‣ https://github.com/barentsen/iphas-dr2
71. 3. Outstanding challenges and future opportunities
72. We would *really* like to finish IPHAS ‣ Need to repeat 1424 pointings (9%), of which 1023 are critical (7%). ‣ This needs 14 *perfect* nights (10 are critical) in November-December grey time. ‣ We secured 10 nights in November 2012, but were met with horrible weather and WFC noise. ‣ We are currently reviewing our strategy ...
73. DR2 is not the end, we want to take the data exploitation further ‣ IPHAS DR3 catalogue planned ~1 year from now. ‣ We are currently bidding for funding to prepare a full-survey mosaic at arcsecond-resolution. ‣ We will also be bidding for funding to continue our data release work, with the eventual aim of building an integrated IPHAS+UVEX+UKIDSS catalogue which exploits PSF fitting.
74. U g’ r’ ‣ Identical footprint to IPHAS ‣ U, g, r, (He I) photometry ‣ The g band, in particular, aids several Galactic science applications.
75. Omegacam VLT Survey Telescope (Paranal) ‣ VST Photometric Hα Survey ‣ ESO public survey, started in early 2012. ‣ Southern Galactic plane (180-by-10 degrees) and bulge (20 by 20 degrees)
76. g’ r’ u’ i’ Hα
77. Conclusions ‣ The biggest program in the history of the INT, IPHAS, is about to release a major legacy data product. ‣ DR2 offers calibrated r, i, Hα photometry for up to 220 million sources across 93% of the northern Galactic plane. ‣ We still need 10-14 good, grey, Nov-Dec nights to finish. ‣ IPHAS DR2 is a template for future IPHAS/UVEX/VPHAS data releases, subject to manpower.
78. Collaboration: University of Hertfordshire (IPHAS/VPHAS PI) University of Nijmegen (UVEX PI) University of Cambridge (pipeline) University of Graz Other members: Instituto de Astrofísica de Canarias, Harvard/Smithsonian CfA, University College London, Imperial College London, University of Warwick, University of Manchester, University of Southampton, Armagh Observatory, Macquarie University, Tautenburg Observatory, ESTEC, University of Valencia. Key individuals: Janet Drew (IPHAS lead), Hywel Farnhill, Geert Barentsen, Robert Greimel, Mike Irwin, Eduardo Gonzalez-Solares, Romano Corradi, Paul Groot (UVEX lead), Danny Steeghs, and many more. Credits
79. More info: www.iphas.org @GeertMcTwit www.geert.io github.com/barentsen