NEWFIRM

NOAO Extremely Wide-Field Infrared Imager

Survey Overview1

Hα nebular emission is one of the most direct tracers of star formation. As such, a great deal of our current understanding of star formation in local galaxies is based on a long and rich history of Hα observational studies. However, there is a dearth of analogous work in the intermediate redshift universe - a critical period in galaxy evolution where the overall star formation activity reaches its maximum - because the line is shifted out of the optical window past z~0.4. Thus, we have begun a campaign to extend deep Hα galaxy surveys to earlier cosmic times by taking advantage of the new capabilities offered by the NOAO Extremely Wide-Field Infrared Imager (NEWFIRM) at the KPNO 4m. Our strategy is to obtain (1%) narrowband imaging of key extragalactic fields in low-OH airglow windows at 1.19 and 2.09 μm (Hα @ z~0.8 and 2.2 respectively). Coupled with IMACS at the Baade 6.5m, which is well-matched for obtaining optical spectroscopy for emission-line galaxy candidates identified in the NEWFIRM narrowband imaging, the data from this survey will enable a wide range of investigations including:

  1. a search for extremely metal poor galaxies (Z< Zsun/12) which are potentially in their initial phases of star formation and/or have lost a significant amount of metals to the IGM via outflows,
  2. direct comparison of star formation rates (SFRs) derived from multiple tracers (e.g., Hα, [OII]3727, GALEX UV) over a broad mass and metallicity range,
  3. examination of dust extinction via Balmer line ratios,
  4. computation of Hα luminosity functions and SFR volume densities, and
  5. large-scale environmental studies of the most prodigiously star-forming systems.

Completeness Simulations

NEWFIRM makes detections by taking images with a narrow-band (at 1187 nm) and J-band filter. The J-band flux (which represents the continuum), scaled to account for the differences in broadband/narrowband filter widths, is subtracted from the narrow-band flux (which represents the emission from Hα at z=0.81 and the continuum), which results in an estimate of Hα emission at z=0.81. Hα is a tracer for star formation rate and since lookback time is a function of redshift we can use data from NEWFIRM to determine the star formation rate for the z=0.81 epoch of the universe. Unfortunately NEWFIRM cannot detect every Hα source so the data from NEWFIRM alone will not result in an accurate star formation history of the universe. To compensate for this, galaxies are simulated with known parameters and then injected into mosaics of science data from NEWFIRM. Then the sources are extracted using the normal method and a ratio of simulated sources to detected sources is found. This is called the incompleteness of the data and can be used to find an accurate count of detected galaxies at different luminosities.

Parameters used to simulate galaxies:

1.      Luminosity Bins [33.4, 33.6, 33.8, 34.0, 34.2, 34.4 ,34.6, 34.8 ,35.0, 35.2, 35.4, 35.6, 35.8, 36.0] in log(Hα/W) the simulations are done once for each bin (the calibration process is described here)

2.      X and Y position on the chip between 50 and 5,350 pixels for both X and Y on the 5,400 by 5,400 chip assigned by a uniform distribution

3.      Equivalent Width log(EW/)=1.17, 1.52, and 2.00 assigned from Lee et al. (2007) with standard deviations also from Lee et al. (2007)

3.      N[II] Ratio The Hα line is brightened to include the N[II] lines according to a distribution from Villar et al. (2008) that assigns N[II] by equivalent width

4.      Position Angle 0-360 assigned by a uniform distribution

5.      Axial Ratio 0.15 to 1 (we estimate 0.15 to be the minimum because of the intrinsic "fatness" of the disk) assigned by a uniform distribution

6.      Half Light Radius R0.5 as defined by the equation -ln(0.5)*( ρ + randn*[ρ /3]) where the disk scale length ρ is 1.18 for z=0.81, the redshift our filter is calibrated to detect, and randn is a random number from a normal distribution with a standard deviation of 1 and a mean of 0

7.      Extinction Extinction is done using the Hopkins et al. 2001 prescription

8.      The number of sources simulated 1,000 sources per image (any more and overlap dominates the statistics)

9.      The Distance Thresholds Coordinate matching is set to 3 pixels or 1.2 arcseconds for these simulations. Also, any source found within 1 pixel of a source detected in the original mosaic is excluded

10.  The Signal to Noise Threshold Set to 3 for these simulations

Parameters used to SExtract galaxies:

1.      Detection Threshold 2.0σ

2.      Number of Contiguous Pixels 5 pixels

After all of these parameters have been determined galaxies are added to a base image by the IRAF task mkobjects. The base image is a mosaic of science data collected by NEWFIRM. The noise of NEWFIRM is dependent on X and Y position on the chip so it is impossible to accurately simulate the noise of NEWFIRM with IRAF and a single noise value. This is unfortunate since this means there is a chance that a simulated galaxy will overlap with an actual galaxy, what we call uncertainty due to overlap (which may also occur if two or more simulated sources overlap as well). To minimize overlap the number of sources per simulation is limited. After the simulated galaxies have been created Source Extractor is run exactly as if the image were a normal science image. Any source which lies inside a mask made up of bad sections of the detector and stars is excluded. The simulated galaxy counts are then compared with the counts from SExtractor. Sources found by SExtractor which are not within a certain distance threshold of the simulated position are excluded. SExtractor is also run on the mosaic image and any galaxies in the image with simulations that are within one pixel of a galaxy found in the mosaic image are considered to be real galaxies and are excluded. Simulated sources which do not have SExtracted sources within the distance threshold are considered non-detections. If multiple SExtracted sources lie within the distance threshold, then the source with the closest magnitude to the simulated source is considered the match. The signal to noise ratio for every matched source is then found by converting counts to flux and then using the following equations:

img1.png

img2.png

Parameters used to calculate the final completeness:

         1. Mask Files Any simulated source within a mask file is eliminated.

         2. Real Distance Threshold Any simulated source within 1 pixel of a source detected by sextractor from the original image is eliminated.

         3. Sextractor Distance Threshold Any simulated source that has no sExtractor detection is considered a non-detection.

         4. Signal to Noise Threshold Any sExtracted source with a S/N less than 3 is considered a non-detection.

The completeness is then detections/(detections+non-detections). We simulate 250 galaxies/simulation/quadrant which ends up around 150 galaxies/simulation/quadrant due to the real distance threshold and mask files. We run the simulation 30 times so in the end there is ~4500 galaxies/field/quadrant.

New Results

Old Results

Extinction Included -Hopkins 2001                                   Extinction Excluded

log(Hα/W) % for log(EW/)=0-2 % for log(EW/)=1-2
33.4 0.7790 +/- 0.0008090 0.6810 +/- 0.001202
33.6 0.9830 +/- 0.001416 0.7460 +/- 0.0007090
33.8 1.498 +/- 0.002585 0.7710 +/- 0.001109
34.0 2.333 +/- 0.002892 1.149 +/- 0.002203
34.2 4.060 +/- 0.006260 2.229 +/- 0.003420
34.4 7.370 +/- 0.009120 4.640 +/- 0.006860
34.6 14.11 +/- 0.02560 11.08 +/- 0.02074
34.8 30.21 +/- 0.04430 26.69 +/- 0.02973
35.0 59.50 +/- 0.05300 58.40 +/- 0.05570
35.2 86.40 +/- 0.02127 86.30 +/- 0.01311
35.4 94.90 +/- 0.004700 94.80 +/- 0.009870
35.6 96.00 +/- 0.01369 96.00 +/- 0.006960
35.8 97.00 +/- 0.006810 96.50 +/- 0.003290
36.0 97.40 +/- 0.003950 97.20 +/- 0.006290
log(Hα/W) % for log(EW/)=0-2 % for log(EW/)=1-2
33.4 0.8780 +/- 0.001541 0.7160 +/- 0.001418
33.6 1.705 +/- 0.002858 0.9480 +/- 0.001706
33.8 2.866 +/- 0.007080 1.409 +/- 0.002875
34.0 6.100 +/- 0.01119 3.920 +/- 0.005270
34.2 13.55 +/- 0.02168 10.27 +/- 0.01996
34.4 34.30 +/- 0.04390 31.17 +/- 0.03340
34.6 72.30 +/- 0.03028 72.50 +/- 0.02521
34.8 93.70 +/- 0.01466 93.00 +/- 0.007180
35.0 96.10 +/- 0.004090 95.60 +/- 0.007100
35.2 96.90 +/- 0.003720 96.70 +/- 0.006250
35.4 97.50 +/- 0.007850 97.10 +/- 0.006940
35.6 97.80 +/- 0.003138 97.70 +/- 0.002855
35.8 98.20 +/- 0.002291 97.90 +/- 0.002905
36.0 98.60 +/- 0.003260 98.50 +/- 0.003370

Extinction Included - 1 Magnitude

log(Hα/W) % for log(EW/Å)=0-2 % for log(EW/Å)=1-2
33.4 0.6130 +/- 0.0008290 0.6680 +/- 0.001497
33.6 0.7720 +/- 0.001516 0.6950 +/- 0.0007420
33.8 0.9850 +/- 0.002119 0.7280 +/- 0.001108
34.0 1.413 +/- 0.002762 0.9400 +/- 0.001625
34.2 2.865 +/- 0.002810 1.535 +/- 0.002885
34.4 5.900 +/- 0.01060 3.920 +/- 0.005930
34.6 12.92 +/- 0.02025 10.46 +/- 0.01001
34.8 34.80 +/- 0.05200 30.67 +/- 0.01981
35.0 72.90 +/- 0.02920 71.70 +/- 0.04520
35.2 93.80 +/- 0.007580 92.90 +/- 0.01360
35.4 96.00 +/- 0.005750 96.00 +/- 0.008700
35.6 96.80 +/- 0.002745 96.30 +/- 0.006690
35.8 97.40 +/- 0.001501 97.30 +/- 0.003820
36.0 97.80 +/- 0.002142 97.90 +/- 0.003360

Extinction - 1 Mag - Lower Right Quadrant                   Extinction - None - Lower Right Quadrant

log(Hα/W) % for log(EW/)=0-2 % for log(EW/)=1-2
33.4 0.9800 +/- 0.001088 0.9650 +/- 0.002233
33.6 0.8110 +/- 0.0007680 0.6840 +/- 2.372e-7
33.8 0.9180 +/- 0.0009470 0.6840 +/- 2.431e-7
34.0 1.451 +/- 0.003860 0.9290 +/- 0.002124
34.2 1.817 +/- 0.004520 1.163 +/- 0.003780
34.4 6.610 +/- 0.04260 3.240 +/- 0.02663
34.6 15.20 +/- 0.05850 10.13 +/- 0.03350
34.8 37.50 +/- 0.08680 34.60 +/- 0.1048
35.0 76.60 +/- 0.1542 74.10 +/- 0.1177
35.2 93.70 +/- 0.007110 93.10 +/- 0.02316
35.4 96.20 +/- 0.01724 95.40 +/- 0.02943
35.6 96.40 +/- 0.03720 95.90 +/- 0.04390
35.8 97.60 +/- 0.02999 96.20 +/- 0.01294
36.0 97.80 +/- 0.007050 98.30 +/- 0.02037
log(Hα/W) % for log(EW/)=0-2 % for log(EW/)=1-2
33.4 0.9670 +/- 0.004380 0.8630 +/- 0.0007150
33.6 1.392 +/- 0.004110 1.049 +/- 0.008140
33.8 2.221 +/- 0.01519 1.409 +/- 0.009280
34.0 6.360 +/- 0.05320 3.380 +/- 0.008880
34.2 15.39 +/- 0.06510 9.300 +/- 0.008730
34.4 35.80 +/- 0.1638 32.30 +/- 0.05540
34.6 75.20 +/- 0.08070 75.30 +/- 0.07660
34.8 93.60 +/- 0.01957 93.30 +/- 0.02187
35.0 95.40 +/- 0.06330 95.50 +/- 0.02290
35.2 96.40 +/- 0.02616 96.30 +/- 0.01456
35.4 97.80 +/- 0.01142 97.00 +/- 0.02517
35.6 97.90 +/- 0.01979 97.80 +/- 0.01215
35.8 98.00 +/- 0.007760 98.00 +/- 0.04730
36.0 98.60 +/- 0.008120 98.20 +/- 0.01235

Extinction - 1 Mag - Lower Left Quadrant                       Extinction - None - Lower Left Quadrant

log(Hα/W) % for log(EW/)=0-2 % for log(EW/)=1-2
33.4 1.122 +/- 0.003000 1.070 +/- 0.001555
33.6 0.9880 +/- 0.003210 0.9230 +/- 0.0007540
33.8 1.293 +/- 0.004020 0.7380 +/- 5.140e-7
34.0 1.456 +/- 0.007900 1.378 +/- 0.005350
34.2 2.750 +/- 0.01327 1.725 +/- 0.008550
34.4 4.620 +/- 0.01735 3.065 +/- 0.008040
34.6 12.98 +/- 0.02528 9.450 +/- 0.06370
34.8 30.75 +/- 0.03270 26.90 +/- 0.07390
35.0 70.00 +/- 0.03870 66.20 +/- 0.07080
35.2 91.60 +/- 0.08010 92.60 +/- 0.04720
35.4 96.20 +/- 0.01870 95.00 +/- 0.04980
35.6 96.10 +/- 0.03600 97.00 +/- 0.01706
35.8 97.90 +/- 0.01479 96.50 +/- 0.02627
36.0 97.60 +/- 0.01799 97.20 +/- 0.05800
log(Hα/W) % for log(EW/)=0-2 % for log(EW/)=1-2
33.4 1.474 +/- 0.002536 0.9660 +/- 0.002406
33.6 1.748 +/- 0.01216 0.9670 +/- 0.001799
33.8 2.030 +/- 0.007270 1.331 +/- 0.005930
34.0 4.210 +/- 0.03072 3.200 +/- 0.03790
34.2 13.32 +/- 0.1052 7.870 +/- 0.1076
34.4 30.82 +/- 0.07140 27.20 +/- 0.1104
34.6 68.20 +/- 0.1238 69.50 +/- 0.1298
34.8 93.40 +/- 0.06470 93.10 +/- 0.05120
35.0 95.10 +/- 0.03700 95.20 +/- 0.02895
35.2 95.90 +/- 0.02849 97.00 +/- 0.02504
35.4 98.20 +/- 0.007030 97.50 +/- 0.01805
35.6 98.20 +/- 0.009550 98.00 +/- 0.01319
35.8 98.40 +/- 0.005090 98.20 +/- 0.02340
36.0 98.70 +/- 0.004850 97.60 +/- 0.03230

Extinction - 1 Mag - Upper Left Quadrant                       Extinction - None - Upper Left Quadrant

log(Hα/W) % for log(EW/)=0-2 % for log(EW/)=1-2
33.4 1.022 +/- 0.003690 0.9200 +/- 0.002432
33.6 1.006 +/- 0.002692 0.8400 +/- 0.0007110
33.8 1.190 +/- 0.007440 0.8930 +/- 0.001046
34.0 2.061 +/- 0.01209 1.466 +/- 0.008030
34.2 3.270 +/- 0.03540 2.931 +/- 0.009200
34.4 5.900 +/- 0.02183 5.190 +/- 0.008230
34.6 15.82 +/- 0.1036 10.48 +/- 0.06050
34.8 34.30 +/- 0.1714 34.20 +/- 0.2146
35.0 72.80 +/- 0.08160 73.10 +/- 0.1873
35.2 94.30 +/- 0.04070 94.30 +/- 0.02053
35.4 95.90 +/- 0.01313 95.70 +/- 0.03030
35.6 97.20 +/- 0.01606 96.70 +/- 0.02253
35.8 98.00 +/- 0.01174 97.60 +/- 0.007210
36.0 97.70 +/- 0.008940 97.80 +/- 0.007020
log(Hα/W) % for log(EW/)=0-2 % for log(EW/)=1-2
33.4 0.8980 +/- 0.001001 1.056 +/- 0.003920
33.6 1.371 +/- 0.001844 1.112 +/- 0.002116
33.8 2.357 +/- 0.01776 1.905 +/- 0.01162
34.0 4.220 +/- 0.02054 5.480 +/- 0.01996
34.2 14.08 +/- 0.1788 9.780 +/- 0.03460
34.4 38.10 +/- 0.2822 33.80 +/- 0.1457
34.6 73.50 +/- 0.05120 72.00 +/- 0.1472
34.8 93.80 +/- 0.06880 92.20 +/- 0.05370
35.0 96.90 +/- 0.007090 97.00 +/- 0.009050
35.2 96.90 +/- 0.008200 96.50 +/- 0.003280
35.4 97.90 +/- 0.006880 97.60 +/- 0.01955
35.6 97.00 +/- 0.01579 98.60 +/- 0.01527
35.8 98.80 +/- 0.005570 98.50 +/- 0.001814
36.0 97.40 +/- 0.007200 98.20 +/- 0.008010

Extinction - 1 Mag - Upper Right Quadrant                    Extinction - None - Upper Right Quadrant

log(Hα/W) % for log(EW/)=0-2 % for log(EW/)=1-2
33.4 0.7160 +/- 0.0003850 0.7490 +/- 0.0002753
33.6 0.8140 +/- 0.001781 0.9380 +/- 0.001405
33.8 1.058 +/- 0.008740 1.075 +/- 0.003260
34.0 2.130 +/- 0.01072 1.422 +/- 0.01211
34.2 2.426 +/- 0.01074 2.438 +/- 0.01536
34.4 5.920 +/- 0.008900 2.777 +/- 0.01321
34.6 13.77 +/- 0.06610 12.45 +/- 0.05250
34.8 32.10 +/- 0.2695 28.93 +/- 0.1749
35.0 70.70 +/- 0.1070 71.60 +/- 0.08290
35.2 93.40 +/- 0.03057 92.80 +/- 0.04360
35.4 96.50 +/- 0.02863 96.40 +/- 0.01903
35.6 97.30 +/- 0.02012 97.40 +/- 0.01052
35.8 97.10 +/- 0.02297 97.50 +/- 0.01532
36.0 98.20 +/- 0.01821 98.10 +/- 0.01284
log(Hα/W) % for log(EW/)=0-2 % for log(EW/)=1-2
33.4 1.022 +/- 0.001984 0.9040 +/- 0.002424
33.6 1.451 +/- 0.006310 1.174 +/- 0.003159
33.8 2.955 +/- 0.01281 1.812 +/- 0.01743
34.0 6.650 +/- 0.04130 3.114 +/- 0.01008
34.2 14.26 +/- 0.03210 10.19 +/- 0.05700
34.4 33.80 +/- 0.1888 29.81 +/- 0.04470
34.6 72.40 +/- 0.1860 72.90 +/- 0.1084
34.8 93.30 +/- 0.04430 91.80 +/- 0.03103
35.0 96.30 +/- 0.009330 95.90 +/- 0.04610
35.2 96.80 +/- 0.01169 96.60 +/- 0.03550
35.4 98.10 +/- 0.01938 96.90 +/- 0.02633
35.6 97.60 +/- 0.01914 97.90 +/- 0.01881
35.8 98.30 +/- 0.01281 98.20 +/- 0.01763
36.0 98.20 +/- 0.01247 98.90 +/- 0.006690

Graphs of the results

Note: Percentages were found by averaging completness found by 25 simulations (we used 25 different random number seeds). The uncertainty is the standard deviation taken from the 25 simulations and has no other propagated uncertainty.

Danny and I have written a small section for an upcoming paper which can be seen here.


In order to test these results a number of plots were created:

 

SExtracted J-Band Magnitudes vs. Narrow Band Magnitudes

Simulated J-Band Magnitudes vs. Narrow Band Magnitudes

Simulated Magnitudes vs. SExtracted Magnitudes

 

 

J-NB vs. NB

 

 

1. Taken from the NEWFIRM wiki: http://newfirm.ociw.edu/wiki/Main_Page

 

Last Updated: April 13, 2010