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Contents 1 Sources of Diffuse UV emission at High Galactic Latitudes - A GALEX Study Using Targets from South Galactic Pole 2 Introduction 3 Observation 4 Foreground Emissions 4.1 Airglow 4.2 Zodiacal Light 5 Correlation Studies of background Emission 5.1 FUV-NUV & IR- UV Correlations

[edit] Sources of Diffuse UV emission at High Galactic Latitudes - A GALEX Study Using Targets from South Galactic Pole

[edit] Introduction

The GALEX spacecraft is an Earth orbiting UV telescope which started its observation since April 2003. The primary objective of the mission are to explore the origin and evolution of galaxies, the origins of stars and heavy elements over the redshift range of z between 0 and 2 and conduct an extra-galactic survey.

Our aim is to use all the GALEX deep observations, with enough exposure time for the study of faint objects, to map the diffuse UV radiation field over the sky. So far we have studied a set of observations near M82 (Sujatha et al. 2009), which is an optically thick region, where Sandage (1976) observed nebulosity and a set of observations from an optically thin Draco region, where SPITZER has made its first look extragalactic survey (Sujatha et al 2010). All these targets are from moderate latitudes of about 36 deg.

In this work, we are using a set of 14 observations with exposure time > 10,000 sec, from high galactic latitudes (between -69 and -76 degrees), in which one is our own observation. The objective of this study is to identify the sources of diffuse radiation towards the south galactic pole.

[edit] Observation

GALEX uses the first ever UV light dichroic beam-splitter flown in space to direct photons to the Near UV (1750-2850 \AA) and Far UV (1350-1750 \AA) micro channel plate detectors. Each of the two detectors has a 65 millimeter diameter.

GALEX orbits nearly circular around the Earth with a period of 98.7 minutes at an altitude between 690 and 700 km (~428 miles), which is above the atmosphere, but below the Van Allen radiation belts, at an inclination of 28.99 degrees to the equator. Right Ascension of Ascending Node is 118.23 degrees.

Details of The observed locations

Sl.No.	Tilename	dstDegrees	ra_cent	dec_cent	gl_cent	gb_cent	nuv_exptime	fuv_exptime	minObsDate	maxObsDate	nuv_Visits	fuv_Visits
1	GI1_005001	0	0.546	-43.124	331.725	-71.145	15055.75	15055.75	2004-10-03	2004-10-15	11	11
2	ELAISS1_00	6.64	9.640	-43.989	310.84878	-72.94075	42207.70	30460.40	2003-09-14	2009-09-25	43	37
3	ELAISS1_01	6.41	9.319	-42.968	313.82904	-75.08024	31313.4	30669.35	2003-09-25	2006-09-02	29	29
4	ELAISS1_02	7.68	11.085	-43.855	307.36582	-73.21209	44652.45	28895.65	2003-09-28	2007-09-26	40	28
5	ELAISS1_03	7.3	10.403	-44.888	308.61164	-72.13173	36952.90	30848.6	2003-10-26	2005-10-13	33	29
6	ELAISS1_04	6.28	8.924	-44.908	311.95458	-71.94345	36442.4	30247.90	2003-10-27	2005-10-12	32	27
7	ELAISS1_05	5.29	7.664	-44.355	315.21060	-72.27444	49766.6	29391.7	2004-07-18	2006-10-05	49	32
8	ELAISS1_07	7.26	10.359	-42.248	309.98137	-74.74307	25951.35	25944.35	2003-10-01	2008-11-15	21	21
9	ELAISS1_08	5.24	7.702	-42.824	316.56308	-73.75393	38397.00	32068.45	2004-09-06	2005-10-24	29	24
10	ELAISS1_11	6.48	9.120	-41.730	312.31066	-73.90140	54907.10	29384.5	2004-07-19	2006-10-06	51	28
11	ELAISS1_13	8.3	11.686	-41.893	306.35426	-75.20405	30640.30	30640.30	2004-09-28	2008-11-12	23	23
12	ELAISS1_14	5.47	7.724	-41.768	317.65265	-74.76790	31900.45	31900.45	2004-09-28	2007-08-24	33	33
13	ELAISS1_15	6.05	8.831	-43.802	312.92579	-73.01220	32157.90	31256.90	2004-09-11	2005-10-12	27	27
14	QSOHE2347	2.13	357.649	-43.434	336.02263	-69.57618	26891.55	10444.2	2005-09-13	2006-10-06	24	12

[edit] Foreground Emissions

[edit] Airglow

The airglow contribution in each field are tabulated below. The possible error bar in these values is about 40 photon units which is mainly due to the scatter in the data. The variation in the TEC minimum during the visits of an observation is due to the foreground contamination which is time dependent. The details are given here[1].

[edit] Zodiacal Light

Zodiacal light contribute heavily to the NUV signal and its value is very much depends on the time of observation and the line of sight. Therefore its contribution will be different for the visits of an observation. Hence we estimated its average contribution (the exposure time weighted average), in each of the observations and are tabulated below.

Exposure time Weighted Average Foreground Contamination in each Observation

Sl. No.	TILE NAME	Sun_Ang to LOS	Solar Activity	FUV AG_C	FUV AG_V	Total FUV_AG	NUV AG_C	NUV AG_V	Total NUV_AG	Variation of (λ − λO) during visits	β	ZL (PU)
1	GI1_005001		89 - 91	306	43	349	333	49.24	382	137--149	-39.04	469 - 492
2	ELAISS1_00	72 - 138	72.4-138.1		39.18			44.63		104.88 - 235.01	-43.25	430 - 460
3	ELAISS1_01	75 - 149			41.48			45.41		86.58 - 233.66	-41.13	430 - 500
4	ELAISS1_02	66 - 149			49.24			45.91		137--149	-43.7	430 - 500
5	ELAISS1_03	78 - 243.4			43.87			46.11			-44.3
6	ELAISS1_04	76.8 - 274.4			48.66			46.09			-43.75
7	ELAISS1_05	74 - 155			59.79			48.91			-42.8
8	ELAISS1_07	66.7 - 221.5			47.23			44.10		136.92 - 161.18	-42.05	430 -490
9	ELAISS1_08	73.4 - 133.4			32.91			43.46			-41.51
10	ELAISS1_11	74 - 170			54.3			47.38			-42.26
11	ELAISS1_13	66.7 - 90			42.85			40.51			-42.27
12	ELAISS1_14	69 - 90			30.84			31.36			-40.62
13	ELAISS1_15	76 - 137			41.13			45.92			-42.78
14	QSOHE2347	76 - 117			47.95			47.87			-38.24

[edit] Correlation Studies of background Emission

Details of Correlations

Sl. No.	Tilename	FUV-NUV	IR100-FUV	IR100-NUV
1	GI1_005001	0.66	0.36	0.44
2	ELAISS1_00	0.30	0.09	0.22
3	ELAISS1_01	0.32	0.50	0.16
4	ELAISS1_02	0.39	0.01	0.07
5	ELAISS1_03	0.44	0.21	0.21
6	ELAISS1_04	0.30	-0.33	0.23
7	ELAISS1_05	0.55	0.14	0.18
8	ELAISS1_07	0.23	0.30	0.22
9	ELAISS1_08	0.56	0.43	0.29
10	ELAISS1_11	0.55	0.70	0.56
11	ELAISS1_13	0.37	0.60	0.35
12	ELAISS1_14	0.56	0.88	0.39
13	ELAISS1_15	0.22	0.04	0.08
14	QSOHE2347

[edit] FUV-NUV & IR- UV Correlations

The correlation plots for each targets are given in the link ELAISS1 Individual Correlations. These plots are generated before the subtraction of foreground emission. Its average contribution in an observation is uniform over the field, and hence its subtraction affects only the axis range of individual plots given here and not the distribution of points or its correlation.

GI1-005001