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Searching for a cosmic string through the gravitational lens effect: Japanese Virtual Observatory science use case

Y. Shirasaki１,4、Y. Mizumoto1、E. Matsuzaki2、M. Ohishi1、N. Yasuda1、M. Tanaka1、S. Honda1、

H.Yahagi1、M.Nagashima3、G.Kosugi1、N.Kashikawa1、F.Kakimoto2、S.Ogio2

(1) NAOJ, (2) TITech, (3) University of Durham, (4) yuji.shirasaki@nao.ac.jp

Abstract

This poster describes a method to search for a cosmic string using its unique gravitational effect which produces aligned double images. Implementation of gravitational lens search to Japanese Virtual Observatory (JVO), which is aimed at the string search, is also presented

5. Gravitational lens search on JVO

- 3. Simulation Study
- We examined ability of the proposed method by simulating lens effect by a cosmic string.
- 3.1 String model
- Three kinds of configuration as shown in Fig.2 (left).
- Mass density 1022g/cm → max separation 5’’.
- Perpendicular to the line of sight.

- 3.2 Galaxy distribution
- The numerical Galaxy Catalog (nGC). Calculated by a N-body numerical simulation.
- Cosmology L-CDM, Wl= 0.7, Wm= 0.3, s8=1

- 3.3 Result
- Maximum redshifts, where cosmic string can produce enough lens events to prove its existence by the proposed method, are calculated according to the observational conditions (Fig. 2 Right).

- We developed several VO tools to implement a gravitational lens (GL) search on JVO prototype.
- JVO Query Language (QL) Editor (Fig. 4).
- VOTable Viewer (Fig 5).
- Candidates’ images and SED Viewer (Fig. 6).
- GL search engine.

Fig. 4

- Introduction
- Grand Unified theory predicts that super heavy cosmic strings with linear mass density of 1022 g/cm were produced at a phase transition at the early universe.
- The lens effect by a long cosmic string can be characterized by undistorted double galaxies and quasars which are co-aligned in a direction of string network and are distributed in a very large scale. Because of its large scale nature, wide fied deep survey is crucial for its discovery.
- We have constructed a database of Subaru Suprime-Cam catalog and image for selected area and applied our search method partially through the JVO prototype.

Fig. 5

This field sets a restriction for a color of R-B

- 2. Method
- 2.1 Procedure
- Select closely located pair objects of similar magnitude, color, and morphology.
- Calculate a degree of positional and directional coherence Cobs for the set of pair objects.
- Calculate 1000 sets of the degree of coherence Csim for a set of randomized pair objects and obtain C99 so that chance probability for Cobs to be larger than C99 is 99%.
- If Cobs > C99, the aligned pair objects are candidates of the lens events by a cosmic string.
- 2.2 Definition of the degree of coherence C

Fig. 6

JVO QL Editor generates a query and send it to a search engine. VOTable is an output format of the search engine and can be viewed by VOTable viewer.

Current version does not support morphological similarity check, so by constraining to a point like object and rejecting stellar-like color, 12 QSO GL candidates are obtained (Fig. 7).

Fig.2. Left: Assumed string configuration. Right: Detection limit of distance to a cosmic string as a function of observational condition (limiting magnitude).

4. Application to the observational data

We applied the method to the data of Subaru-XMM Deep Survey （SXDS). No candidates of string lens event were detected.

P2

Fig. 7

P3

P1

Fig.3. Left: Positional and directional distribution of the pair objects. Right: Degree of coherence.

Fig.1. Definition of parameters.